Update and Append Tilesets...

One of the things that I have a lot of trouble with is updating my tilesets. When imported, it appends the whole tileset to the end of the existing one, all I want to do is update them. I've been travelling to the resources folder and combing through the stuff there to find and update it, and sometimes the changes don't stick. Is there a better way to do this, or is this something on an updated feature list somewhere?

I find it very frustrating editing tiny details of my tileset because of this too.