After airborne departure of the first leg of the rotation, anything changes….flight is removed….flight is added….changed form operate to DH or vice versa…it’s a Reroute.

Highly recommend you read Negotiators' Notepad 24-03: Reroute Rules and Pay Treatments because not only will it tell you what’s a RR or not, it’s will tell/show you how to calculate your RR pay, which I assume will be your next question.