Function that works like MSExcel's SUBSTITUTE in Rules and TI.
You have an acceptable workaround in TI, but it gets so much harder to live without it when it comes to Rules as described in this thread:
http://forums.olapforums.com/viewtopic.php?f=3&t=2860
Possible syntax (based on MSExcel): SUBSTITUTE(text, old_text, new_text)