Yes:
Many times over the past 8+ years. As a matter of fact I've spoken with Bill Stine directly about this method of converting standard MMX motors into booster motors on at least two occasions. He concures completely, as far as encouraging it as a great way to Stage micro motors/models.
At Naram-50 we were talking about staging again and I mentioned it'd sure be nice if He and/or Quest would issued a tip sheet on converting standard to booster motors using this safe and easy method. If this happened, it would no longer be considered altering the motor and Should be allowed at any NAR sanctioned launch.
He the said "Oh man John I sure wish you'd reminded me about the a month ago..... we could have had the last 50k or so, MMX-II finished without the delay or ejection charge...No problem". Well crap! I said and we went on talking about several other staging issues, this sort of side tracked me from getting back to weither or not Quest would issue such a the tip sheet...DOH!!
But back to your question.. with it I've gone from the rather disappointing 30-35% upperstage ignition rate to about 95% success. I've still had a couple fail to ignite but they were taped together method rather then Gap staged or even semi gap staged which i've found over the years is a more reliable method then the taped together method.
Why don't you send Bill an e-mail asking about issuing a booster conversion fact sheet? maybe if enough OTHER micromaxxers make the request he'll follow thur with either the memo or producing a booster motor

Hope this helps.