I made a proof of concept for swapping out perk trees in game effectively letting a mod add more than the vanilla number.

https://www.youtube.com/watch?v=UkCobiQWIn4&feature=youtu.be on youtube showing the vanilla one-handed perk tree in the regular menu and then the SPERG one-handed perk tree replacing the werewolf tree and finally the normal werewolf tree.

Its just a rough proof of concept at the moment and I used the werewolf tree because I first thought that would be needed but I don't think it is. Getting new perk trees into skyrim is a pain and needs fiddling in tesedit.

By the Nine, that's amazing. Now this just allows for additional perk trees right, not additional skills? If I remember correctly there are no unused actor values in Skyrim, so adding new skills would be harder, correct?

On its own yeah. But you should be able to fake a new skill in a script and then before they swap to the perk tree set its value to match what you tracked in the script and the perks would be pickable based on that.

Looks amazing, it would greatly expand the gameplay if it is made possible.

What about the background?