Well, it's more like doing design stuff and getting back into doing art at a more regular basis; IE- remodeling my old ships and such from my sketchpad into Blender3D models. But if it's a like-within-like, for example, physically working out during a physical job/manual labor is a no-go during work-hours (Only real exception being if I'm doing creative work while cleaning, and physically exercising while doing graphic design work), it doesn't count. That should clarify things a tad.
It's basically a way of preventing me from cheating the system by using work as an excuse of fulfilling the Lent task/sacrifice.
EDIT:
Of course, the mental exercise is continuing to learn programs like Blender, keep rust off of programs like Illustrator and Photoshop, coming up with new ideas and concepts, and applying them/debugging applications of ideas (Like with this new ES-RM thing), and so forth. Games, unless sufficiently challenging may somewhat count, but they have to teach me something new, or refine my skills in the process (like reaction timing and such; Race the Sun could work, to a degree on reactions, but it would have to stick with me to count; but that's giving games an excuse to count, which seems a tad unacceptable, since I'll just be playing games, instead of doing something productive.).