Modular PCB design in Altium
You should use device sheets for that. See the respective wiki article. You have to play around with the naming conventions in the settings dialog, as not all combinations seem to work properly...

Convert your current schematic into a device sheet, then instantiate it multiple times.

Combine this with the pcb snippet feature to allow for rapid placement of pre-routed designs, e.g. power supply, op amp and so on.

The suggested manual act of copying, re-annotating, replacing, possibly re-routing is the poor man's equivalent, but much more time consuming. Depending on the design, initial setup and learning curve quickly amortize.