At least two that i'm aware of:
1. Set manual maintenance schedule using Inventory explorer - Navigate to Administration -- Inventory explorer -- select hosts -- use maintenance button above to enable/disable maintenance schedule
2. Use powerCLI (version >6.3 R1) - you might take a look here: http://www.virtu-al.net/2016/08/10/working-maintenance-mode-vrops-via-powercli/
3. Create CG with you hosts, add policy, add maintenance schedule, apply policy to hosts.
I would rather use 1 or 2, depending on number of hosts and your confidence with Powercli.
Using the manual mode might be the best option if hosts are rebooted at different times or if the maintenance windows are not always at the same time. Here's a link to a nice explanation on how to do this: https://blogs.vmware.com/management/2016/06/working-with-maintenance-mode-in-vrealize-operations.html
It also covers setting up schedules if you di have regular maintenance windows so you can set it once and let the schedule automatically put hosts in vROPs maintenance mode
Depending on how you have your policies set up, you can disable the alert in the policy during the time frame as well. This also has to be done manually, and would apply to all objects under that policy.
I suppose you could build a custom group, and attach a policy which has alerts totally suppressed. Just add the host or hosts you plan to upgrade to that custom group during the change (manually), and remove them afterwards.
I'm not sure that this is any better or easier than previously mentioned suggestions, but it is an alternative.