Bought a 07.5 LMM tuned and modified by previous owner need advice on vcm editor

[caseyreed76]

I bought an 07.5 that was *modified* and tuned by previous owner years ago. I put a 52 gallon tank in it, and just want to edit the tank values in hptuners. I was able to read the ecm in vcm editor without issue, and modify the tank size and sending unit table. However, I am hesitant to upload the tune, because I dont know how it will play with the codes that HP tuners doesnt allow you to view or edit. I dont want to brick my ecm, or cause other issues. Does anyone have any guidance? I just want everything to keep working as is if possible.

[caseyreed76]

Does HPtuners just ignore the missing settings? I am trying to find out if just changing the fuel tank settings on the current tune which was *modifed* years ago, then writing it will cause the missing settings to reset to defaults?

Somebody has to have some insight on this.

[Stroked06Goat]

In my experience (one truck LMM) It will run it as you brought it in. So those settings not seen...will remain as is as HPT doesn't 'change' them on their own without intervention yourself.

[caseyreed76]

I need to be 100% sure before I do this, so I just want to verify that in your experience with LMM ecm, if the truck has already been *modifed* in the past, and the existing tune is unlocked / readable by current hptuners software, then all of the forbidden settings that no longer exist in hptuners will be left as is when I modify the tune and write it back onto the truck.