I Need Advice On Taking Over A Sheet

So I've been making edits on the 4th edition version of the L5R sheet for months now. In that time, I've been posting my edits here and trying to contact all the people who've been making edits on the sheet, trying to get their permission to take over maintenance. I finally have permission both from the original creates and the person who's been making current commits. Here's the problem: in the time this has taken, I've made some pretty massive changes. Implemented sheet workers. Reworked a lot of things under the hood. Reworked a lot of the rolling mechanics and variable logic. This has been pretty well tested on my campaign, but to no one has ever replied to any of my threads in the forums, so to my knowledge no one has ever actually tested the sheet on a long-running L5R campaign. I'm afraid if I put out a pull request, something unforeseen will happen and it will break a bunch of campaigns and a rollback will take weeks. Anyone have any experience with this? Any proceedure advice for me?

You could update the current sheet to include a note about coming changes (and a link to your thread), and recommend Pro users test it out on a copy of their game. After that gets pushed out to current users, wait about two weeks, then push out the new sheet and major changes. If that garners no feedback, and depending on how much you want to test this, you could do the same as above but offer a "bounty" in the note on the current sheet for the GM of a current L5R game. Maybe offer 1 month of Pro subscription to them if they will GM you in a copy of their game.

Create a beta game and try to get people to test the sheet.  You might also enable importing characters(character vault), so that people can import older characters created from the older version of the sheet.  If you change any existing attributes, you may have to include a migration function in sheet workers to prevent breaking existing sheets. Test as much as possible.  Once you think you have a working sheet, release the changes.  Be prepared to fix anything that breaks.  Also be prepared to take the wrath of anyone that doesn't like your changes.  ;-P

I highly recommend the creating a sheet construction game room and letting people in it to look and test the sheet out. I did that with my sheet and I'm still asking feedback on my sheet (which means accepting criticism) and I'm still finding typos in the sheet. 

Thanks for the advice. I have a campaign people can test on, but since no one has ever replied, no one knows about it. I had it in my head that you could only buy Pro a year at a time, so I had thought of a bounty, but in my head it was cost-prohibitive. At a month, that's a whole other story. I think that's my route. Buy someone with an old campaign a month of pro membership, have them copy the campaign and test the sheet.