I'm not 100% certain if the system will even allow you to change the conversion metric after the activity has been started. If it does the risk will be that inevitably at a later point in time someone will look at the conversions and compare the latest conversion metric "carrots sold" with "carrots sold" in Analytics and wonder why they don't match. (The answer will be because it was originally counting "beets sold" and then was later changed to count "carrots sold" but they won't knwo that) Hope that helps illustrate why that is not good practice. The system will not be able to overwrite past data as fi the new metric had originally been selected. If you decide to change the metric after you activate the activity my recommendation would be to do the following: a.) De-activate existing activity. b.) Clone it. c.) Add somethign in the name to help differentiate it. d.) Modify the conversion metric in the new activity. e.) Activate that new activity.