Won't work, as SE already tried this very idea with FFXI years ago - it only stopped the RMT for a week before the gilsellers realized what was being blocked and thus they simply adjusted how they wrote the url in the tell (substiuting certain letters like 'w' for numbers, and including directions on how to access their RMT site within the tell.).

It basically shows that no matter what RMT do, it's a never-ending battle where a change is made to stop them which the RMT find ways around.