Random Questions I have and things I want to do

It's good that you have ideas...but a lot of these ideas are highly unrealistic. In order to modify the game you have to know how the game works, and once you peel back the layers and view the disassembly, it becomes clear that there are hard limitations to consider. Contrary to what people often state, it is not really possible to do anything with modifications.

For instance, to tackle one of your ideas.

6. Have Runic only work against enemy-cast spells, persist when used until it consumes a spell, then recover MP equal to the spell cost of the consumed spell and temporarily add the consumed spell to the characters spell list until the battle ends (OR add a % learned to that spell on the character's spell list).

The first three steps have been done already and are relatively easy fixes, but the fourth step (adding consumed spell) is going to be near impossible unless you ENTIRELY recode how the spell list is generated in battle.

Final Fantasy VI sets all available spells for the entire party at the beginning of a battle, and it does this, more specifically, by eliminating unknown spells. The battle system does not even check for the list to be modified in the battle "loop" so there's no structure to even account for a dynamic spell list.

Plus the in-battle magic list doesn't display partially learned spells, so it's an all or nothing propsect, but that's minor compared to the dynamic availability issue.

Now even if you want to limit it to "Runic Use = Learn Absorbed Spell or Percentage" after battle, you still have to come up with a way to track which spell was used, set a flag to be set upon a successful Runic, then add extra code to do this post-battle. This is much more doable but still not easy.