We've been to Boma on Xmas and TG (2006 and 2007).
On TG 2007 they had a station with turkey, cornbread, cornbread stuffing, mash, sweet potato mash, cranberry sauce, green beans and gravy and then the regular food with some dessert alterations (pumpkin zebra domes i think and some pumpkin flan thing).
Now, we've never been to Boma on a non-holiday night, so can't tell you how much was replaced. However, having read the menus and seen people's pics, certainly when we went it seems much of the Boma stews/ curries were taken out, but they had most of the salad/ cold items they normally have.
I think they swapped out quite a few of the hot items for the big beast of the turkey they were carving
Oh, and when we made our Boma ADR for 2007, the CM I spoke with told me there wasn't really going to be any TG items...so not sure if it might be the same incorrect info this year??

Personally I'm glad they did the whole TG meal - that was some of the best food I've eaten on WDW property!!