I would suggest limiting it to those 1st place uniforms involved in winning the BC. Only that uniform should be "retired", all others retaining eligibility.
I agree. A Grand Muster first place uniform will be "retired" from future uniform competition. It may be worn again, just not for competition.
A Division Muster first place uniform can be used for the Grand Muster, but not for another Division Muster.
Major modifications to the uniform so that it is a completely different uniform may be allowed, such as removing all the infantry trim and replacing it with cavalry trim, however the competitor will have to declare that this was done. Just replacing the rank will not constitute a major change.
Individual components and accessories of a winning uniform can be reused. This might include a belt, buckle, sword, watch, gloves, and other items that were worn by more than one service, corps (branch), or uniform regulations (such as the 1851 belt plate).
We should also remember that competitors competing for BC, should be wearing a uniform complementary to the firearms they are using. Judges should take this into account so that a really sharp looking Civil War soldier carrying an 1884 trapdoor may have points deducted. This means that if a competitor wins first place in the uniform competition but does not win BC, they will have to come up with a new uniform in order to compete for BC again.