Decommission a vCMP guest and reallocate its cores to remaining guests

Fore removeving Guest you can do it without restriction. Once you remove Guest you have to remove Virtual Disk:

• On the Main tab, click vCMP > Virtual Disk List.
• Locate the Virtual Disk List area of the screen.
• In the Name column, locate the name of the virtual disk that you want to delete.
• To the left of the virtual disk name, select the check box.
• Click Delete. The system prompts you to confirm the delete action.
• Click Delete.

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/vcmp-viprion-configuration-11-4-1/7.html

however, when you will reallocate its cores to other remaining guests, you must pay attention:

If you have a guest that's actively processing application traffic and you decide that it needs additional CPU cores than its original core allocation, you can increase the number of cores per slot for the guest. To do this, you'll need to temporarily disable the guest while you add cores, and then re-deploy the guest.

Follow this procedure: https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/vcmp-administration-viprion-13-1-0/7.html

Regards