google for panelization or multi panel - several threats also here in forum manufacturing partition. There are commercial non trivial tools specialized for this task with several import export move rotate features linked in the other threats. Unfortunately Kicad cannot cover this for the moment. Nevertheless, there is only small diffrence between Gerber and Excellon file format if you like to contribute code therefore. Mainly the file headers are completly diffrent while the formats can be easily converted to each other. Some links are also where I struggled with drill format here: Reverse Workflow