in-game there are items that boosts the skils bats/summor gargoyle. I wonder, can this be done for other vanilla/custom spells?

like "ring of explosions: when worn, your Fireball spell has doubled radius and damage".

This is not my area of expertise but when worn that ring would have to grant you a "perk" or temporary ability.
I haven't looked into creating custom perks so I'm not sure if its possible, if so this shouldn't be too hard.

of course custom perks can be created, otherwise what would mods like Skyrim redone or Requiem do?

I don't use either of those mods so I didn't know.

I heavily suspected it could be done, but I could not actually confirm it. So thanks.

look here
http://skyrim.nexusmods.com/mods/9286#

and here
http://skyrim.nexusmods.com/mods/19281

I doubt I am wrong