I think it also depends how close the previous style is to your new style. I just started in a different Kenpo variation from where I earned my black belt (maybe 30-40% different), but I am still wearing my black belt in these classes. The reasons are kind of two fold, first my new instructor respects the work I did to earn my black belt (and my black belt was earned 2500 mi away so even though theschool name is embroidered on I am not avertising for a school someone around here could go to). Second I find it makes it easier on the other students, especially the white and yellow belts, because they are learning something, having lost of problems, or doing it with no precision or flow and see me do it and having few to no problems, even through I am new to the school, and they get discouraged (I've had comments about it so not just tooting my own horn), I find the belt is just something easy to point to or to remind them that , hey, I've been doing this for a lot longer than they have, and even though some of the techniques or forms may be new, many things like the kicks, punching, sparring etc, cross many styles of martial arts with few changes.
That said, I also attended just the white-orange class, for a little over two months when I started and am now splitting my training between the white-orange and purple-green classes. So even though I have a black belt I am not necessarily training with their black belts. I see it as I currently don't have the knowledge or current skills to rightfully join their brown-black classes. Plus it had been a few years so always helpful to have some time to get back in shape :uhyeah: , cause god knows I was always pushed physically and mentally more in my black belt classes than any other classes. In the end I will end up testing for a 1st degree/dan in this system, at which point I won't wear my first black belt anymore, unless I find myself back at my first school. (Besides wearing my black belt all the time saves me from most of their belt testing fees too cause I am not really changing belts :boing2: )