Not that there is any point to it, but it should be possible. I hit level 19 and realized I'm still getting 1 EXP when I do lv17 modules, so I'll get there eventually. PS: It looks like when you hit level 19, you get a fifth Minor (blue) power token. Edit: Actually, it looks like there is a little bit of use to being level 19 and possibly level 20. At 19, it's not scaling me down for level 17 modules so I can replay those with the extra power token. Potentially pretty useful for finishing those challenges.
