I am hoping someone else has already developed a workaround for this particular issue. This is the last hurdle in an otherwise useful script to assist in our CoB (or DR) plan. Replicated VMs are spun up at the DR site in a specific folder in vCenter and once online I'd intended to use this script to modify NIC settings and reconnect them to the VM Network, leaving staff available to handle the SQL box that everyone depends on and other manual tasks. The same goes for failback, and of course proper error handling is a must as well as checks to ensure that VMs native to the DR site do not have their settings modified. Several days ago I'd found a script online that tackled a portion of what I intended and as such it was a great starting point. Now I have a script that meets all of my needs, with exception of replacement of the default gateway. Actually without this piece, the rest is basically a waste of time 
I've tried both of these methods and while I can utilize remove-ipaddress to remove only the current IP address and use set-netipaddress to add a new IP and gateway, I still end up with the orphan gateway. viewing the output of the remove-netipaddress and remove-netroute and you see why they fail: Powershell is in non-interactive mode and as such prompting is not supported, nor apparently can you override prompts.
$scripttmp = 'remove-netipaddress -InterfaceAlias "' + $intAlias + '" -IPAddress ' + $currentIP + ' -PrefixLength 24 -DefaultGateway ' + $curGateway + ' -Confirm:$false -ErrorAction SilentlyContinue'
$remnetout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
OR
$scripttmp='remove-netroute -interfaceindex ' + $intIndex + ' -NextHop ' + $curGateway + ' -DestinationPrefix ' + $DestPrefix'
$rnetout=invoke=vmscript -ScriptText $scripttmp -ScriptType Powershell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
Any assistance is of course much appreciated.
Thank you for jumping in Lucd! I admit I was hoping to hear from you. In short, yes but not precisely that command so I will try that once I've finished this reply.
This is a heavily modified version of a script from herseyc, if it helps I am including it here. Note the lack of error handling, that's coming once this hurdle is cleared 
Failback method is just going to be a matter of minor adjustment to variables based on the "Failover" argument.
In its entirety so far:
###################################
# Parts and pieces from herseyc script for changing IP addresses on 2012 VMs
#
#
param(
[string] $VCenter = "faux-vcsa",
[string] $User = "localadminuser",
[string] $Pass = "localadminpassword",
[boolean] $Failover = $True
)
$ErrorActionPreference = "SilentlyContinue"
Import-Module VMWare.VimAutomation.Core
Import-Module VMWare.VimAutomation.Common
Import-Module VMWare.VimAutomation.Cloud
Connect-VIServer -Server $VCenter
IF ($Failover-eq $True) {
$oIP = "10.10.50."
$nIP = "10.10.60."} Else {
$oIP = "10.10.60."
$nIP = "10.10.50."
}
###############VARIABLES###############
#Original IP to replace during failover"
$origIp = $oIP
#New IP Information
$newIp = $nIP
$newMask = "255.255.255.0"
#$newGateway = "10.10.60.10"
$newGateway = $newIP + "10"
$DNS1 = $newIP + "22"
$DNS2 = $newIP + "19"
$DNS3 = $newIP + "21"
$DNS4 = "10.10.60.60"
$DNS = "$DNS1,$DNS2,$DNS3,$DNS4"
$WINS = @($DNS1,$DNS2,$DNS3,$DNS4);
#$DNS = "10.10.60.60,10.10.60.22,10.10.60.21,10.10.60.19"
#$WINS = @("10.10.60.60","10.10.60.22","10.10.60.21","10.10.60.19");
#Guest Credentials - Must have required permissions to change IP address
$GuestUserName = $User
$GuestPassword = $Pass
# Get all VMs in the recovery folder that are powered on.
Write-Host "Getting list of VMs from COB Folder where state is PoweredOn"
$VMs = (Get-Folder "COB" | Get-VM | where {$_.PowerState -eq "PoweredOn"}).Name
foreach ($vm in $VMs) {
Write-Host "Working on $vm"
#Get relevant NIC
$scripttmp = 'Find-NetRoute -RemoteIPAddress "8.8.8.8" | select-object -ExpandProperty InterfaceIndex -Unique '
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
$intIndex = $scriptout
#write-host "Interface Index = " + $IntIndex
#PowerShell used by Invoke-VMScript to retrieve current IP Address
$scripttmp = '(Get-NetIPAddress | where-object {$_.IPAddress -match "' + $origIp + '" -and $_.AddressFamily -eq "IPv4"}).IPAddress'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
$currentIP = $scriptout
$currentIp = $currentIp -replace "`t|`n|`r",""
#write-host "$currentIp is the current IP Address"
#Adjust Original IP to Replacement IP
$changeIp = $currentIp.replace("$origIp", "$newIp")
$changeIp = $changeIp -replace "`t|`n|`r",""
$NewIPObj = [ipaddress]$changeIp
$NewGWObj = [ipaddress]$newGateway
#Write-Host "Changing IP to $changeIp"
#Get the Interface Name (Alias)
$scripttmp = '(Get-NetIPAddress | where-object {$_.IPAddress -match "' + $origIp + '" -and $_.AddressFamily -eq "IPv4"}).InterfaceAlias'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
$intAlias = $scriptout
$intAlias = $intAlias -replace "`t|`n|`r",""
#write-host "The interface name is $intAlias"
#Get current gateway
$scripttmp = 'Get-NetIPConfiguration -InterfaceAlias "' + $intAlias + '" | Select-Object -ExpandProperty IPv4DefaultGateway | select -expand NextHop'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
$curGateway = $scriptout
#write-host "The current gateway is $curGateway"
$scripttmp = 'Get-NetIPConfiguration -InterfaceAlias "' + $intAlias + '" | Select-Object -ExpandProperty IPv4DefaultGateway | select -expand DestinationPrefix'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
$desPrefix = $scriptout
#write-host $destPrefix
#$scripttmp ='remove-netroute -interfaceindex "' + $intIndex + '" -NextHop "' + $curGateway + '" -destinationprefix "' + $destPrefix + '" -confirm:$false'
#$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
#$rmGateway = $scriptout
#write-host $rmgateway
#$scripttmp = 'new-netroute -interfaceindex "' + $intIndex + '" -NextHop "' + $newGateway + '" -destinationprefix "' + $destPrefix + '" -confirm:$false'
#$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
#$ngGateway = $scriptout
#write-host $ngGateway
#Remove IP address
$scripttmp = 'remove-netipaddress -InterfaceAlias "' + $intAlias + '" -Confirm:$false'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
write-host $scriptout
#Set new IP address and gateway using newer cmdlet
$scripttmp = 'new-netipaddress -InterfaceAlias "' + $intAlias + '" -IPAddress ' + $changeIp + ' -PrefixLength 24 -DefaultGateway ' + $newGateway
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
write-host $scriptout
#Clear DNS / WINS Servers
$scripttmp = '%WINDIR%\system32\netsh.exe interface ipv4 delete dnsservers "' + $intAlias + '" all'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType bat -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
$scripttmp = '%WINDIR%\system32\netsh.exe interface ipv4 delete winsservers "' + $intAlias + '" all'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType bat -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
#Set DNS
$scripttmp = 'set-DnsClientServerAddress -InterfaceAlias "' + $intAlias + '" -ServerAddresses ' + $DNS
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType PowerShell -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
#write-host $scriptout
#Set WINS
#$WINS = Get-WmiObject win32_networkadapterconfiguration | where IPAddress -eq $changeIP
#write-host $WINS
#$WinsSet = $WINS.SetWINSServer($DNS)
#write-host $WinsSet
$count = 0
foreach($server in $WINS) {
$count = $count + 1
Write-Host "Setting WINS Server to $server"
$scripttmp = '%WINDIR%\system32\netsh.exe interface ipv4 add winsservers "' + $intAlias + '" ' + $server + ' index=' + $count
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType bat -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
}
#Connect vmNic
Get-NetworkAdapter -VM $vm | Set-NetworkAdapter -StartConnected:$true -Connected:$true -Confirm:$false
#Register with DNS
#Write-Host "Registering with DNS"
$scripttmp = '%WINDIR%\System32\ipconfig /registerdns'
$scriptout = invoke-vmscript -ScriptText $scripttmp -ScriptType bat -VM $vm -GuestUser $GuestUserName -GuestPassword $GuestPassword
Write-Host "Finished with $vm"
}