I've found out some information but still can't work how to do what I want.
This page explains that the tvservice doesn't work on pc's its just a hack to stop crashing.
I found this on the wiki detailing how to change the display resolution.
https://github.com/recalbox/recalbox-os/wiki/Change-display-resolution-on-x86---x86_64
This is a global change and I would like to be able to set a per emulator resolution. I imagine this could be done using a launch shell script to call xrand and then open the emulator.
How does recalbox do this normally?
Is there any way to edit the existing launch commands to insert an xrand command?