Adding a temperature offset in firmware so I can use the same gcode across multiple printers?  

Adding a temperature offset in firmware so I can use the same gcode across multiple printers?

I have 2 Prusa MK3s - one with an MMU2s and one without. I built both of them and they use the same nickel/copper nozzle, blocks, heaters and temp sensors. The one difference is my non-MMU2 one uses the "standard" E3D heatbreak in case I want to print HTPLA. I built these both from kits as well.

I've noticed that the surface finish of the two is noticeably different even when using the same gcode. One is nice and shiny and the other more of a matte. I did some tests and the difference appears to be due to temperature - if I bump up the temp by 5C on the one that is producing more of the matte finish, it looks a lot closer to my other printer. This is with the same filament (Atomic Deep Black PLA).

While I can just write out gcode with this accounted for, that means I can't swap SD cards between them and have to export models for each printer. So I'm wondering if there is a way to simply set a temperature offset so if the nozzle temp says 215, the printer sets it to 220.

Any thoughts on the best way to do that?