Change Project in Activity

What about to make project a read-only field after activity creation ?

I don't think it may be a good idea, because it often happen that you create an activity (of other item) on incorrect project and want to change it afterwards.

I agree this may lead to unconsistency, but this already exists without changing project :
- you can delete allocation to project for responsible or for assigned resource
- allocation to project may end (end date reached) with same result
- you can select a reponsible through magnifier icon and select a resource that is not allocated to project.
As you see, there may be lots of such unconsistency, and I don't think it is ourpose of tool to control this.
Project manager should know what he does...

So I see two options : the code is able two correct all inconsistencies or the manager drops the current activity and reenter all data in a new activity linked to the right project.

Yes, projeqtor does this !
But as I described previously, this may lead to have real work (and planned work) for resource not allocated to the project.