There is no native way to do this in HCX without redeploying the WAN-OPT appliance.

Alternatively you could use rate limits on the IX vNIC, or use NIOC if using Bulk Migration (ensuring not to put the IX and the VM being migrated on the same host.

https://chrisdooks.com/2020/11/03/using-powershell-to-limit-and-change-hcx-bulk-migration-speed/