How hard would it be to have a function to hide less used spells, instead of deleting them? I ask, because some spells that use less mana can still be useful in situations where mana becomes scarce. On the other hand, after a while the list of spells can get too large.

I think the spell would need to be noted, deleted, then backed up with some pretty precise scripting. I don't know if they can truly be hidden.

EDIT - Or better, something similar to Darnified UI where you can branch and unbranch spells sorted by school or magicka used, or something.

EDIT 2 - I think another opinion is needed by a more experienced and veteran modder.

This looks like a job for MenuQue! (And someone who knows how to use MenuQue.)

Seriously, I'm pretty sure it's possible now, and MenuQue is the tool for the job. The relevant experts are TNO and Kyoma, though of course whether they have time to tackle the project is another question entirely.

A reasonable alternative would be for someone else to become an expert! (Not me!)

Great! Thanks for your input. I will put it on my list. I have so many ideas, its hard to stay focused on one. If someone wants to take the idea and run with it, thats ok with me too.