Okay I figured out how to play Splatoon online atleast for now without updating or risking to update:
1: Block the update with your preferred method
2: Load Splatoon
3: Go to the lobby and let it sit on the screen where it asks you to receive the latest news
4: Disable your block and let then let Splatoon go on
5: Quickly enter the lobby in Splatoon and select the game-mode you want to play
6: Then block the update again
As long as you don't close the game you should be able to play Splatoon normally now