Phil, One may approach this in two different ways. But generally speaking, like in this case, it's recommended you are using a PDM system, such as Winchill PDMLink, for proper data management so one part modification is controlled by one user, to avoid conflicts. Any way, you may work in subassembly levels so that way there will be no conflict. Another way is to use external simp reps (simplified representations). So basically you create simp reps in the top level as you normally do and extrenalize them into separate .asm files (still associative to the top level.) One user may then open one of the external simp reps (created in manner to include some desired components), make modifications and save. Ultimately, the top level will update to those modifications. What you described is typical scenario for what we use top-down design approach for. I'm guessing it's essential you look into it.
