Not able to change registry number on the T-5 Multi Vector Assault Escort Ship after upgrading them. This is only affecting the MVAM Escort. I did try it on other T-5 ships and could still change registry.
I did contact customer support on this matter, the GM told me to post it here. I also posted this a few days ago in General discussions. Original Post:
https://www.arcgames.com/en/forums/startrekonline#/discussion/1264848/multi-vector-assault-ship