I have two local numbers with two different area codes. I am trying to change number A to number B so when I send text from my desktop app the number is coming from B instead of A ...how do you do that?
The ability to do this depends on exactly which numbers you want displayed and if you are the operator. Here's a related topic, that may or may not match what you are trying to do.
Caller ID of SMS to show Main Number
If you can clarify the phone numbers you want to switch back and forth with, and if you are the operator, then we can provide a more detailed answer. I'll make this a private conversation so you can post numbers.