My experience with this kond of changes:
If you are ticketed AAA-BBB-CCC with a connection (no stopover at BBB) and the same airline for both sectors and want to change to a AAA-DDD-CCC (same airline as above for both sectors, no stopover) they never required a reissue.
Boarding passes where stamped, handwritten extra coupons issued etc....., typically easy.
If you change airlines or have a stopover then it is different.