To your account, no. Understand that they can not access anything in your account such as your asset library or any purchase material. You can share the compendium per game basis. When you upgrade a player to co-GM, you are giving them control of a specific game and all the contents inside that game and nothing else. If it is not placed in that specific game, such as journals, handouts, graphic assets in the form of tokens, tiles, and maps, they can not access anything of yours. Outside the game, they have very limited access also. They can moderate, in a limited form, the game forums (main and LFG) and the API scripts. I believe that is about all they can have access to.