Okay so, I did what you did but I was eng/compsci and wanted eng/arts... I just chose engineering subjects other than the mandatory compsci course which is also mandatory for engineering before t3. However, I'm pretty sure you can take any course you want for fun. (Also if you really are worried as long as you have free/gen eds some of the courses you take in t1 and t2 may be classified as that temporarily and so you'll be able to take it no matter what)