Go to the graphics file in the reborn folder, inside there there is another file called battlers. Rename whatever sprites you want to 658_2 (for the front facing sprite) and 658b_2 (for the back) (I'll attach the sprites I use with the water shuriken if you want to use them). If you want shiny do the same but make sure the name is 658s_2 and 658sb_2. if your using the sprites that come in the zip then just drag out the graphics folder into the reborn folder, it will automatically add the sprites. And I'm guessing you already know how to install the base mod.
PS: I don't have shiny sprites sadly.