In the future I would like to modify the firmware to act as both a laser burner and 3D printer while only swapping the printer head. Has this already been reduced to a simple fix or will I have to brush up on my coding skills?
About a year ago another user installed a Duet in his laser cutter, see https://reprappro.com/2015/06/16/reprap-duet-electronics-running-a-laser-cutter-guest-blog/ and http://forums.reprap.org/read.php?133,521301. This didn't require any firmware modificiations and I guess you should be able to achieve what you've been planning by doing the following steps:
1. Add an extra tool with an unused E drive (haven't checked yet if M571 requires one to be configured, but I'd assume so)
2. Run M571 in the tool change macros of your new tools. That way you could enable and disable this particular feature for a specific tool.
3. Use G10 to set the offset of your laser