Unless I'm missing something, The short answer is that the ID number should
never change for a given vendor. Yet you imply that you have changed vendor
id# for a given vendor. And so the short simplistic answer would be to
stop doing that, and, where you have already done it, pick one as your main
#, and go to any duplicates and mark the "double entered by mistake.

I'm sure that there is another aspect to this that you need to tell us about
(= why did you changed ID #s?) in which case the answer might be different.

Hope that helps a little.