Often I need to change an assembly that connects to 2 WEPs into an assembly that requires 3. This never reframes correctly with the new WEP and usually requires alot of manual fixing.
The best fix I have found is to delete the old assembly, select the WEPs, and add the new assembly, but even this adds new material to the poles associated with the WEPs and requires manual fixing. If WEP selection could be incorporated into the "change assembly" feature I think it would fix the issue.