There are 254 possible offsets in Mach and you can easily set them up, if just needing 2 you would be best to keep G54 for the scribe and use G55 for the torch or vice versa depending on which is the one used first or most.
How you would set things up is move the scribe to a point and set the axis zero then move so the torch is over the same point and then in MDI type G55 and hit the enter key then you can zero the axis again and that is you just set up the G55 offset.
You can then change back to G54 and you will see how far away the scribe is from where you set zero.
All that then remains is to call the offset from G code when required, ie when scribe make sure you are in the default G54 offset and when you want to use the torch call a G55 from your code to change to that offset.
Hood