Hello and congratulations for your great work. I am trying to create a variant of your mod with my own considerations. He would give me permission to do so. I have good ideas to improve it and would appreciate even your help. All credit to you for your work of course.

-Casus Beli: Take the crown
If the cohesion of the Imperial federation is negative or one of its members has a "Normal" power relative to the leader of the federation, the winning member can declare war on the president of the federation to get the presidency. If he wins the war he becomes the new president and all the former vassals and the past president become his vassals now.
-Remove the ability to invite any empire to join the imperial federation
-Eliminate the possibility of the president leaving the federation or kicking out any members.
(Alternative: if the above suggestion is not possible then, if the federation president leaves the federation then the entire federation disintegrates and automatically all his vassals are freed. If he expels a member from the federation, he automatically also frees him from being his vassal)
-If possible, add a federation law that allows the president to choose whether the entire federation should participate in the wars or, on the contrary, each nation can wage its wars separately.

What about as a perk, the Emperor, so long as their subject is also in the Empire federation, has a loyalty bonus in terms of subject agreement negotiations (I.E. they can get away with ‘demanding more’ from them)?

Maybe the Emperor can also get some unique Overlord Holding buildings, like souped up versions of the vanilla ones, but they can only be built so long as they’re the Emperor and their Subject is also in the Empire.