First Read up on hierarchical Design and Annotation because I think my explanation is not very good and you will get there yourself easier...
I am not sure your version of Altium limits you in this regard, if you can make hierarchical design you should be able to do this.
Create one Main sheet, next create your sheet where you actually put the electronics and drag it onto the Main sheet so it gets to be the Child of the Main sheet.
On the Main sheet Place a sheet symbol and set the secondary schematic as its Source.
Copy and paste that Sheet Symbol with different _1 termination as designator.
Select for Annotation $ComponentPrefix$ComponentIndex.$RoomName
That should genereate for example R76_1 R76_2 per sheet.
Good Luck

On a sidenote I find the Annotation in Altium powerful but not very intuitive.