Love it,

But would be cool to add a configuration to disable the acid rain messages without needing to give the permission to the user.

Hello, I have not tested the plugin because I no longer have a server at the moment. I rate the idea as very good, I download the plugin and the link for a future server.
Otherwise here may be possible additions:
- Being able to choose a percentage of chance that the rain is acidic or not (this general setting will allow it to be used even on other world generators which do not use Minecraft Biomes)
- Being able to choose a white list and a black list of Biomes which will or will not be entitled to acid rain (with perhaps a percentage of chance of acid rain per biome)
The biome settings should have priority over the general setting that I noted first)
- Being able to choose the worlds that will have acid rain with whitelist
Good continuation