If you already own the assault cruiser and you want the refit; just custamizeit to look the same for Energy Credits

you can't use the new assault cruiser skin without first buying the retrofit. Once you do that though, you can use the skin and the special console/torpedo on your normal Assault Cruiser

That said, if you already own the refit there's no reason not to use that instead of a free AC.

True. Though the BOFF slots are a bit different. You lose a rank on one of the Engineering slots, but gain a universal slot.

It depends on what you want/need. In terms of the special consoles/weapons/Regent Ship skin - you very much could pull all that over to the original Assault Cruiser and mod it to look like a Regent. You could even do the same with a Mirror cruiser.

IMO it's situational. I'm testing out a Regent right now and I'm liking it. But I can foresee circumstances where I might want to go back to my regular Sovereign.

As always, YMMV.

only flaw with the refit over the default assault cruiser..... the defaults RA level and the refit is VA level, meaning you cant just claim the regent as soon as you hit RA and use that instead of the standard AC.