Well, cutting off the saucer and the nacelles is arguably the easiest possible cutting job, involving cuts at the narrowest part of the ship - this is why the model got incorrectly put together in real life!
And Starfleet seems to have done a somewhat similar repositioning with the E-E for the movie Nemesis, plus a much more extensive change in the secondary hull contours of that ship. And never mind the immense amount of work that went to altering Kirk's old ship...
I wouldn't declare the odd refit unrealistic as such, then, not by Star Trek standards.
And if we can argue that there were two different Ambassadors
in "Redemption", we have done our bit in helping, if not explain then at least alleviate
the mystery of why this supposedly successful class is rather underrepresented in comparison with even older designs...