You are allowed to use Badlion Client and Laby mod, you can find the rest of the allowed clients and mods here, you will need to click the Allowed Mods section though. If you feel like something is missing from the list make sure you to talk to a Senior Mod+, before that though, make sure you ask yourself this. Does this give me an unfair advantage? Does this give me advantages that other players don't have with a vanilla launcher? If it doesn't then it's most likely allowed on MCC.