Hello BeginnerinAras,
The first thing I notice is that your start state for your Part Life Cycle is listed as "Start", but the parts you're attempting to mass promote are in "Preliminary." This is quite possibly because the parts were made before you set up your new life cycle, but it means they aren't in a recognized place for your life cycle.
The target field being disabled is odd though, because usually there would be some error. I haven't been able to reproduce that- can you show me how your life cycle is configured? I'd suggest making a very quick life cycle with two states and a transition between them, assigning that to parts the way you've done, and seeing if you can access the target field on that. If you can, that strongly points to the problem being with the life cycle and we can look at what specifically might be causing it.
Skyler C.