For a 2013? Read the manual. It'll display on the dash if you do the right procedure.

 

You can also read it with forscan. So you can’t do squat if you’ve purchased a used truck besides swapping out the module?

 

Correct.
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Are you sure? I didnt have the factory code card in my owners manual booklet. I cant say that my truck was ever programmed by any of the two previous owners, but i used the two key method to get the factory code to display in the dash.
https://seventrumpet.com/easy-way-to...try-door-code/
I would think this would work even if the truck it programmed to an owner specific code. Enter factory code and program any code you want.

 

But you can't change the factory code. Both the factory and the user programmed codes will work in the situation you described. OP is asking how to change the factory code, not add a user programmed code.