I think it is reasonable to have mods require PCs to give heads up via a thread post somewhere for common collection or a PM to make sure. I sure wouldn't want to start self modding a thread in under water basket weaving only to be told that all under water basket weavers are shot and hung on display in public for three days... after I started the thread.
I dunno, I always find it common courtesy to poke mods before I do anything outside of social interaction with other PCs that might be noteworthy, like starting training threads or having ideas for something I'd like to explore, etc. Touching base is just a courtesy but I can see it being a requirement to make sure everything stays kosher in a location, if that sort of thing is outlawed, or would be harder, or would cause you to be chased by an angry mob... or its something you have absolutely no relation to (in Gillar's example a PC that has absolutely no magic history might need to find a book or talk to a NPC for guidance, or a varying number of things so they understand it if they've never encountered it before imo) the skill you are trying to learn.
So yeah - after your clarification there, I totally agree and I think H's suggestion is my preference. That way you guys dont have to track down everyone and instead they come to you saying hey - im gonna do this, is that okay / do you have any suggestions on how i should go about it in your city/wilderness?
*shrugs*