From my "limited understanding", "tunes" as we call them actually just partially rewrite the ECU, some of the sub-routines within the program are rewritten and some are not. I do know there has been 3 different stock ECU tunes from RAM for the 2018. There is a possiblity that the "newest" tune has some of the sub-routines in different memory locations. So, if you try and rewrite a sub-routine for the EGR it could be changing something in the idle section of the program....you don't know, nor does anyone else unless they have hacked all of the ECU each time RAM changes each year of the stock tunes.