There might not be any rule saying that it can happen - but the rule is very specific. It states that only Primary List players can be put on the LTI list.
In any case, if Greenwood were upgraded and they needed to upgrade Keath, then they could just downgrade Greenwood again.
Believe that the Problem with the Cat B once promote they cannot return to Cat B status but have to be Cat A.
The Shaw situation is a one-off due to the AFL and AFLPA inability to finalize an agreement ie Special circumstances and permission may be/should be given.
A lot of rules are in theory null and void between the lapse of the old agreement and new agreement being sign. The main reason most businesses reach an agreement before the expiry date of the last agreement has been reached.