The groove diameter might be undersized- as currently .45 Colt has a .452" groove diameter.
This is not insurmountable as any .457/8" grooved lubricated bullet can be run through a .452" sizing die without damage. The trick, is to simply to size & lube it to .457" first.
Thus, a simple re-chambering would be necessary. Annealing the brass every 3 or 4 shots would help with longevity of the brass. It would be susceptible to splitting otherwise, from the extra work.
Quite possibly, the brass would only need belling & not expanding after sizing, due to the smaller diameter bullet.
The pilot on the reamer would have to fit the smaller bore, of course.