Redundant pair by adding a second BIG-IP VE to an existing system

Sounds like the bigger answer to your need is scheduling a maintenance window. Besides that, clustering works exactly the same as a physical f5, the article you reference is talking about the failover cable, which isn't used anymore.

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/tmos-implementations-12-0-0/3.html

For the vm, I would disable the NICs and then run a config-sync and verify everything is okay. This can be done when it is forced offline if you like.