Bart and Lisa change their appearance with each other and goto school? Will principal Skinner allow new Lisa's pranks? Will Mrs. Krabappel doubt new Bart's A+++ grade? It's quite a good idea more than crazy.
I always get many ideas, some are just flashing by, and some are just drawn immediately like this one. But when I try to make it bigger, like comics, it's always just passed memories although I noted the idea.