Re: second idea- I'm pretty sure this is already a thing. I know in Ethereal, only crops can be broken. I've almost accidentally broken glowstone before, but it wouldn't let me (whoot.). Sometimes there are issues with trees being replanted, but I think that's other leaves being in the way or some weird thing like that.

Totally agree on number 1 though.

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Find a way how to let town mayors see who broke the blocks in their town farm so that they can find out the person who committed it and kick them from the town before that person can do any more damage.
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Longer term I don't see why we couldn't bring out a tool to allow something like that. We already collect that information about block breaking, so it is definitely possible for that sort of tool to exist, but it's just how to give you the option to access that. For now though just ask a member of staff and I'm sure they'd be happy to let you know.

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Make it so in town farms, mayors have a command to change the plot settings so that only crops/trees can be destroyed or placed.

As others have already suggested that is already a feature that was added during the change over to Noobstowny last year. So you can do that already.