Incidentally, skimming through the mafiascum website you linked to, one setup that they seem to have tried multiple times that may be worthwhile to explore here is the so-called "friends and enemies". The only special role featured (ie. besides the required rogues and innocents) are "Masons", who are similar to rogues in that they know all other Masons immediately at start of game and can PM amongst themselves during night. But they have no special powers to directly discover anyone else's role or affect anyone's abilities and alive/killed status, and therefore are just like innocents in all other aspects. This setup might be interesting to try in that it is slightly less plain than having only rogues and innocents, but not having the game too easily affected by the luck of a lone detective (ie. miner) role. You can search the website to find the page on it and the relevant distributions of roles to use for that setup.
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As for the "cannot un-vote once majority reached", I'm unable to find an explanation around it on that site, but it is clear from reading through game transcripts that with all participants fully aware of the implications of the rule, it simply becomes an ingrained element of gameplay and participants will act and react accordingly cognizant of the point-of-no-return, with reaching N-1 being a big deal (and votes cast leading to N-1 or N under more scrutiny accordingly). Instead of casting a vote and pulling back later, you might instead say that you are inclined to vote someone without actually casting the vote immediately, instead using that threat to elicit responses, defenses, etc. from that person and others. I think one negative effect of not having the rule is that a lynching can potentially be more easily derailed by last-minute vote changes.
