Single Master / Transform custom paramater?

Hello Font Friends

This is what i would like to do - is there an easy way to do it, perhaps with a customer parameter applied at export?:

Example:
I have a font with 1 Master.

When I export this font i would like to also export an additional weight (exact copy of the master) but with the horizontal scale set to 50% so it creates a faux condensed. I can then make changes to my original master and these changes apply to both weights at export.

Thanks,
Anth

That can be done with a transform filter custom parameter. Open the transform filter, set it to the scale you like and then copy the Custom parameter from the gear button. Then click in the instances > Custom parameter and paste.

Thank you Georg, that worked perfectly

Anth