Thank you for the reply, Jenop2.

Correct me if I am wrong - but it seems to me that, given all of that information, the best way to accomplish the transition from 'unmodified parts' to 'modified parts' is to simply add the modified parts to the main system's BOM directly (which, again, is an assembly which only has the unmodified part in it's BOM). Then, when we execute a build for the system, then the transition will take place.  By transition, I mean removing one unmodified and adding one modified.

I was trying to execute builds on each of the modified parts to make this transition happen, but what I seem to be running into is that it wants to execute the build for this subassembly whether or not an on-hand quantity exists for it.  

For example:

I have a ring bearing, let's call it item 1234 - and item 1234 is an assembly which references 1234-NPP.  We purchased 3, we did our modifications, and then I ran the builds for 1234 which raised it's on-hand quantity from 0 to 3.  Of course, 1234-NPP on-hand quantity went from 3 to 0.  However, when I try to build the main system which references 1234, I am seeing 1234-NPP on my shortage list.  I am quite confused how this could be.

It seems it's ignoring the fact that an adequate on-hand quantity exists and is still trying to execute the build anyways.

Seems like it should be an option somewhere to, ultimately, "use on-hand quantity when available" or something to that effect.

I hope I am communicating my issue adequately.  Thank you for your insight.