Oh OK, you mean the ones that you can select to move into a lot. To edit them, you would need to pick them to move into a lot (even just a temporary game file will do) then once in the game, using testingcheatsenabled, click on the sim - not sure if it's left or right click, and you should get the option to edit them in CAS. Once there, you can edit them and save them to the library for further use.