I've seen a few tests that were to figure out how critical having the end of the barrel squared truly is.
In one test they even cut the barrel off at a 45° angle. Point of impact changed, but group sizes remained constant.
What has an effect on accuracy is if there is a burr on the edge (transition) of the crown (right where the rifling comes to an end).
As long as it is crisp and burr free, I doubt you'd see much/any different if the barrel isn't cut perfectly square.
I have a few rimfire rifles I have shortened with a chop saw and re-crowned with one of those fancy "Acorn" decorative nuts (covered in lapping compound). Accuracy is as good (or better) with the new crowns than the old.
My truck/beater brush rifle is a Mosin 91/30 I chopped the stock, bedded, slugged/shortened the barrel and re-crowned. With winchester/S&B ammo my groups went from about 3" average at 100yds to just under 2".
I used the chop saw to trim this barrel, and used a carriage bolt and 280 grit valve lapping compound on this crown.
My point?
Try it yourself, and leave yourself a smidge of lee-way. I bet you'll be satisfied with doing it yourself--if not, as mentioned above, you left enough barrel to have smoeone else do it again.