How do you edit the function comment on a custom method?!?!?!?

[josborn]

Can't be done, at least not yet.

Script Custom Method - Parameter Documentation

This isn’t currently possible, but it’s an interesting idea… Script editor refinements are on the short list of improvements; while this wouldn’t land in that initial round, I could see it coming as a further enhancement - maybe a table for the parameters, where you could also define an expected type and a comment.