I recommend that you use Toolbox. It's a bit more difficult to use than Static.pack hack tools but still easy to use. You simply open the static.pack file with this program, extract the file you want to modify, modify it, replace it inside the static.pack file using the same program, and then save the static.pack file to the same location as the original.
P.S. If you have any Splatoon updates installed on cemu, you will need to modify the static.pack file for that update as well, otherwise the modification will NOT work.