Yes I've done this when we installed a new 8400 pair and a 9450 pair.
We got a test scenario from HPE via our re-seller/installer which seems to work and can be done from the office (rather then pulling wires in a data center).
As mentioned it's a timing thing, this method needs hitting return on a command on the source array CLI and on the Witness VM CLI as close together as possible (I had one open on PC and other on laptop so could hit the keys at the same time).
Basically you use controlport on the source array to down all the IP/FC Rcopy ports and use an iptables command on the Witness to block traffic from the source array.
We've only done this when in early test phases with a selection of VMware/Windows/Solaris test hosts connected. If you wanted to be really brutal I guess you could down all the host ports on the source array at the same time (the command takes a list of ports so you can do them all if wanted).
I too would expect some of our 'well written enterprise' apps to trip up on SCSI timeouts.
In a live environment we've only done a manual switchover of PP groups when preparing for a DC power down and that went smoothly.