They can program it anyway they want.
I chose a very simple example.
I think the best way is a toggle switch that says:
Disable friendly requests
That way you can still initiate friendlies, but not accept them from anyone.
If you want to accept them, then just hit the toggle switch and then you are open to all friendlies, wanted or unwanted.
the problem Nordeus has is determining what friendlies are wanted and what are unwanted. Only the manager can determine that, and for Nordeus to allow the manager to pick and choose who to accept friendlies from on a single manager basis is a bit harder to program.