SOE provides the ability to extend map services. You cannot change them.
You can hook the underlying data via ArcObjects itself. Perhaps you could define a custom feature class. This starts to get deep fast and takes you down a path that will cause you pain in the future.
There is no built-in mechanism which allows you to do this.
One possible solution is to develop a custom proxy to which you direct ArcGIS Server requests. In that proxy you can intercept and override messages as needed.
There is no built-in mechanism which allows you to do this.
One possible solution is to develop a custom proxy to which you direct ArcGIS Server requests. In that proxy you can intercept and override messages as needed.
In 10.3.x you can use the custom soi (Server Object Interceptor) . See page 8 in http://proceedings.esri.com/library/userconf/proc14/tech-workshops/tw_689.pdf .