if i change this, will this reset the odometer? meaning i need to add the odometer of the previous miles + the new one?

 

also let's on the NEW guage cluster, if it reports "30k miles" and the previous had 60k miles, so i add those 2 up? when purchasing a new guage cluster, does that mean i get brand NEW miles (meaning it starts back up at 0)

 

The guage cluster is responsible for keeping track of the miles, not the ecu. So, if you DO buy a brand new cluster, with 0.0 on the dial, you will need to write down somewhere what the old cluster said. If you ever plan to sell the car, this pay pose a problem. One option is to go to a notary. They can actually give you a notarized slip telling the original miles on the original odometer. Hope this helps.