Making mercenaries occupy immune is a straight nerf in my opinion as that puts them in the possible NK category and makes sorcerer’s job easier to fake being a mercenary to evil. They will also lose their occupy immunity if converted to ritualist, so overall really this will hurt mercenary players win rate in my opinion.
Occupiers need to do their job too and you cannot just make almost all classes occupy immune.
Rebound thematically is not even important to the Mercenary as a support role and I rarely find myself making use of it in my Mercenary games. Having it have some of the suggestions above also allows Mercenary to kill the king. Something which I find extremely undesirable.
Mercenary is one of the classes that I hardly lose with. If you really feel it’s a weaker knight, you’re just not using the social aspect of the game to its fullest extent. Mercenaries will generally be left alone, by either side, as you have at least one other player pulling for you to live, your contract. More than that they can choose their allegiances as the only class, barring neutral king, in the game freely, by allocating their second contract.