Can I substitute shortening with margarine?

May be.
Check out this link. Peace!

Community - CookingLight.com - Substitute for shortening?

I don't know if you're supposed to... but I do it all the time and things usually turn out just fine. I can't think of anytime where it really messed up the recipe (my cookies come out flatter when I subsitute, but they still taste good). What are you making?