Updates are not allowed until Mousey has played them on stream or the voting and prescreening process would need to be done all over again
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.
I think a good solution for that would be to let people decide on their favourite games, then give the devs like a couple of days or a week to update the games if they want to, and only after that check them, so that noone gets in anything nasty.
Like, again, in the Monke Jam, Monkeet did get into the stream with an update, which means that the mods didn't check the games immediately after the voting was over, hence devs should have a period to be able to improve their upcoming "judgment by Mousey and chat day" experience. After all the monke jam stream didn't happen right after the voting period ended, it took a few weeks, so maybe with this one there should be some time as well.
I do see why now this is a complicated question, since it wasn't considered before, but i hope that if there are going to be more jams in the future, that this question will be answered in the rules from the start. Like I understand the concern of the hosts, since it's their first game jam (most of them didn't even have an itch.io account before), but the updating post-voting period really shouldn't be one of them, as it's not a problem in the wast majority of other game jams. With this one being so similar to the Monke Jam, and that one also did not have a problem with updates. :D