Ummm...maybe I'm not following you here. If I'm reading right, your logic is....I'm a 3rd degree in Kenpo, yet if I went to a BJJ school, I'm learning as a 3rd degree? No, nobody can take my rank away from me. I busted my *** for it, its mine until the day I die. However, if I go to another school, I'm starting from ground zero. Sure, the inst. will most likely acknowledge your rank from the other art, but frankly, I wouldn't want to wear the same rank, especially if I'm doing another art. If I were to start taking TKD, I'm wearing a white belt, not my Kenpo BB.
I switched from the Parker system to the Tracy system. Yes, I still wore my 3rd degree. Its still a Kenpo system, and many of the techs and katas a very close. My teacher told me to wear my belt, so I did. I didn't strut around though, as if I was a 3rd in that school. Once I completed the material that that school taught, I tested for a BB in that system in that school.
Of course, the purpose of this thread was to discuss being awarded rank in an art that you've never trained in. For example...I move to California and go to a Kajukenbo school. The inst. at that school, knowing that I have a MA background, but not a Kaju background, hands me a 3rd degree BB in Kaju, complete with diploma. I call BS on that one. Why? Why the hell would I want to wear a belt that I didn't earn???? IMO, only someone with bad intent does something like that.
If you want to recognize someones acomplishments in the arts, and give them some honorary thing, thats fine, but that person should NOT under any circumstances, lead people to believe that they put in any blood, sweat and tears, into that belt. Doing so, would give a false impression.