I have never actually tested this, so I'm not sure if this actually works. It seems that the AI Scripts for computer difficulty, Easy, Medium, Hard, Insane, are all "Run AI Script at Location." Does this mean that a single computer could have several bases, some that are easy, some hard, etc.?
I don't know how to find out directly so I've been experimenting.
I tried running 5 different scripts at seperate zerg bases. Expansion Zerg Campaign Area Town, Easy, Medium, Difficult, and Insane in various orders. In any order of execution the indivudial bases develop in much the same way, the way you would expect them to develop if you had only run one script. The Easy base is slow and builds hardly anything, the Area Town base only mines resources, the Insane base pumps out units and fills in it's area with buildings as fast as possible. This seems to suggest that you can run multiple ai scripts for a single computer, however there are differences when you run the scripts in different orders.
Getting right to the point: The last script you run dominates.
When I had the Insane ai script run last the computer was extremely agressive, it acted like an Insane computer overall. When I had the Easy ai script run last the computer was laid back with it's attacks and slow to climb the tech tree, it acted like an Easy computer overall. Using an Area Town script dosen't seem to have any effect on the computer player's "mood" though.
Also, attacking the Easy base was a peice of cake. It's like the computer was AFK. Attacking the Insane base, on the other hand, was very difficult. The computer defended it's harder-ai-script bases much better than the easier ones. (It only sent one zergling to protect it's Area Town base, it sent EVERYTHING to protect it's Insane base)
So uh, yes and no.