We would like to be able to change the REST name of web services in Portal and AGOL.
There is documentation indicating this could be possible but after testing it with ESRI analyst (case 02552145), renaming the REST name has not been possible.
The documentation is:
Rename Service with ArcGIS REST API (doesn't work)
How To: Change the name of a feature service (changes only feature layer)
Update Definition (Feature Service)—ArcGIS REST API: Services Directory | ArcGIS for Developers (payload doesn't stick)
This idea change is related to the following post: