Pre-Mute Direct Outputs are not a standard jumper option on the GL2400 mixer.
It would be possible to individually modify each channel to hard-wire the direct output to a pre-mute status, but this would be a custom modification that would not be carried out at the factory.

This would need to be carried out by a service centre or a qualified engineer.

We would recommend consulting your local A&H distributor regarding this.
They may be able to advise on a company or individual who may be able to carry out this retrofit for you.

Please note that modifying the mixer would likely invalidate any warranty remaining on the unit without the express consent of your distributor responsible for the warranty.