@Riot, is it still possible to make custom Login Screens?

I've been a big Jinx/Vi/Ekko enthusiast since their respective releases, and generally use their Release Login Screens and rotate my way through them every fortnight or so. With the new client, however, I cannot locate the folder that all the Login Screen Images and .flv loops held in. Have you compiled them into un-editable files or are they sitting somewhere else in the game files?