I don't really see why the voting would need to be redone, since the top 20 would already be decided and it would allow the finalists to fix anything they wouldn't want the stream to see. I guess we can't avoid the comparison to the Monke Jam, ran by Connor (CDawgVA), LordKyubae and StellenCopy. One of the winners of that game jam, "Monkeet" by "byXToGo", had an update before Connor did his stream with the jam submissions, which allowed for a better game and stream experience for both Connor and his viewers. And this update did not loose byXToGo their #10 spot based on the voting period, since the rules didn't say anything against it. And just like with Monke Jam, Mouse Jam's rules specifically say that the updates aren't allowed DURING the voting period (...you may not submit any work or updates during the voting period.), and there's not a single word about post-voting period updates. And changing the rules mid-voting would be kinda nasty, since everyone has already read the rules on the main page of the jam, why would anyone re-read them and find a new rule? And you can't expect everyone to read this specific community board...
Another great example would be "monke girlfriend wants FRUIT!" by "Brewed Leaves" and "MatcheboxMox", who are actually participating in Monkey Jam with "Cutie Conquest". These devs have made some small bugfixes DURING the voting period. And they still got the #12 spot and got to be played on stream on Connor.
And if someone who doesn't get to the top 20, updates their game and it becomes awesome and considered by many to be worthy of the prize or being played by Mousey, well too bad, since THAT IS against the rules, cause it didn't get into the top 20 DURING the voting period.
Also if the top 20 games (aka the results tab) will be hidden initially like with the Monke Jam, there won't be a way for devs to tell that they've made it to the finals, so they'll have little to no ulterior motive to put in something nasty in the game, knowing that they'll get to show something that wasn't planned on stream, cause they won't know that they'll make it to the stream.
I guess it's mostly my opinion, but if it'll be considered i guess it'd be really nice for the devs, since quite a few of the participants who I've talked to want to make some animation or performance or bug fixes. It's not that they're submitting a drastically different game, they are submitting a BETTER experience with the SAME GAME.
TLDR - Post-Voting Updates aren't forbidden by the rules, and if they are now, they shouldn't be, cause the updates wouldn't interfere with the voting results and would allow for a better stream and overall jam experience for everyone involved. Also banning them now would be pretty much impossible, cause not every dev is gonna see this community post.