Trimming the shaft make the club lie flatter, assuming you setup with the same posture. It won't make the lie angle change one bit.
To the OP: Being short like that, I would go see a clubmaker, don't buy off the rack sets and have them modified. Since you are going to take your first lesson, you don't even need a whole set, ask the clubmaker to build you a 7 or 8 iron, take your first few lessons with it and see how it's feel. Don't worry about lie angle or anything else, just get them feel right swinging. Most of the time you will find the club too heavy or too light, or too imbalance (head heavy or shaft heavy), tell the clubmaker, he will make adjustments accordingly.
I made a bad decision switching to steel shaft irons without trying them out first and now have to spend $$$ going back to graphite, way too heavy for me. Go see a clubmaker or at least try before you buy.