Mafia: general discussions.

Does the moderator forbid it? If it's not obvious from the game that a player is clearly not playing the role they're pretending to be, and it's also not clear whether they definitively belong to another faction, then it's acceptable.

Okay, so the town reveals its roles, and then, based on the results of the night actions, confirms those reveals.

Punishing both sides for revealing roles is excessive; forbidding the Mafia from lying when their survival often depends on it is also excessive.

It's not about not lying; it's about clearly revealing themselves as another role.

Punishing only the town for revealing roles is foolish for the reasons mentioned above, but it's better than nothing.

It's not better. The rules shouldn't be different for different sides.

However, in our games, only Tox reveals roles; the others play fairly.

Many players reveal their roles to some extent. But if we're talking about Tox's merits, it was he who popularized the practice of fully revealing a town role when it's about to be eliminated.

Is it okay for a team to "modkill" a player who, during the day, supposedly revealed a Mafia member as a townie to gain an advantage? If someone is so bothered by reveals (even if it's just one player, haha), then they can be punished through external methods: sanctions or being excluded from the next n games, but not by "modkilling" or issuing warnings during the current game.

If you like reveals, false reveals, and pretending to be other roles, then go play psychological Mafia; what's the problem?
Don't mix everything together. In evidence-based Mafia, you can use other methods to deal with negativity: framing people with false evidence, using night actions or skipping actions, etc.
The issue here is different: the town should never be allowed to give obvious hints about their roles – this is what really makes it difficult for the Mafia to figure things out.

sanctions or being excluded from the next n games, but not by "modkilling" or issuing warnings during the current game.

Isn't "Adeptus" disruptive to the game?

there's a huge difference between revealing and pretending

In theory, yes. Ideally, if you're pretending to be a role, you should only do it through your own behavior. But it shouldn't involve giving hints.