I have an ad group with a long history and a high historical CTR. This helps in placement and allows me to bid lower than I otherwise would. So that's good.
If I change the URL to modify some tracking code, will this be considered a change in the ad? And if so, will that mean my historical CTR will be wiped away? Because I don't want to go back to the default CTR used in calculations for new ads, as that would require me to bid higher to maintain a decent position.