Does it make it easier for a stock duplicator if the pattern stock (including Bondo) is finished? If so, what is suggested - paint, varnish etc.?
Thanks.

I never used finish on patterns, just smooth them up before trying to cut a stock blank. Several patterns were altered to make the dimensions that the body of the customer needed for correct fit. My stock duplicator was made for the shop only and I never cut blanks for others to do the final fit.

Way back when I had the NorthStar Duplicator (now sold) I spray painted the patterns with black epoxy for a smooth finish.

I made the tracers for roughing cuts with a Teflon tip.

Both made for easy work in the duplicating.

Coat of paste wax and a teflon guide tip

Yes; I have painted them, varnished them, waxed them. Doesn't matter unless you used balsa wood. Bondo does need paint though as it is not slick.
I made some today and used it on an M38A1. That is a jeep.