What are you talking about!? You can change your champion splash arts at will! The loading splashes requires a bit more work, but is perfectly doable.
I gave Graves his cigar back (I got so fed up with that joke, it was actually what made me find out how it's done).
http://oi65.tinypic.com/wcib5u.jpg
I also reverted the King of Clubs Mordekaiser splash art (not that I will ever buy the skin myself):
http://1.bp.blogspot.com/-fHc57YnEWSg/VUpggYd6KCI/AAAAAAAApgA/HJkBhsejNIw/s1600/MordekaiserLoadScreen_5.png
...it got changed because some religious softie took too many in the feels by the cross, so it got changed. It was all the reason I needed to go back to the "illegal" version shown above.
https://pbs.twimg.com/media/CGhJa-pVIAAa1oR.jpg
Zyra, Fiora, Kayle, Sivir, DJ Sona, Vayne, Shyvana, Irelia and likely more, which I can't remember off-hand, have recieved either a new splash art or a reversion.
"I hack because I can; I mod because I must!"
VO mods, custom login screens, custom skins, mapmods...I do all of the above. And all of it verified within the game regulations.
With that out of the way, I wanna whine too about how PAX Sivir got ruined with her rework.
Fair enough, her model was clunky and her kit outdated, but her PAX skin actually looked better pre-rework.
It used to look like something from Tron: Legacy, with sharp contrasts and a fancy look...now it just looks like something from the original Tron movie from 1982. It looks, in a word, "dull", like most other things in this game with the current graphics style.
Yeah, I want the old SR back too. And the old Fiora. And lots of items.
Also, Sivir's old dance was better: It made no sense, but still looked cool - the current one just makes no sense...
And Sivir's current champion selection emote is so cringy, it makes me wanna throw stuff at my speakers! So that's next on the mod list to make go away (reversion, preferably).
https://www.youtube.com/watch?v=MZLYgMvzmzg
So if you want a nude Ahri splash art, I can make that happen.
No, I haven't done that (I DO have a life), though one did ask for a NSFW Vi splash once, which I still got a copy of.
Hell, if you want to replace a specific splash art with a kitten, I can send you the necessary files.