Hi Jo,
I don't know the answer I'm afraid, but am just bumping your post up so that hopefully someone else will see it.
I have read lots of anecdotal stories of band -to- bypass and band -to- sleeve conversions, and all successful from what I have read.
I know there are a few ex banders on here who have converted to a bypass, but in most cases several years later, and the ops were done at separate times.
Hope one of them will be along soon to help you.
Best wishes.