I don't think it would - technically the default was always 100, and since that doubles as the max right now, all existing character WADs will have values less than that. Thus compatibility with those WADs would most likely be maintained.
Unless the designer was retarded and actually left it at a number higher than 100, in which case you'd notice them being able to jump higher all of a sudden. Worse things have happened, I guess.
EDIT: Oh, right, you meant compatibility between 1.09.4 and a would-be 1.09.4b. Duh.
Yeah, well, that I can't really answer for you.