Permanently scale complete file and setting scale to 1?


I’ve got a file here which apparently was modeled in feet and inches. Still units are set to meters.
Everything is wrong by a factor of 2.54.

Here is what I’d like to do.

Scale the complete scene by 2.54
Somehow permanently APPLY this new scale (!!!)
Than set the scene scale factor to 1 and metric
Continue with the correct metric values

How is this done?

The reason are that I sometimes need to unify models from different sources which sometimes have issues like mentioned above.

In large complex scenes it is to complicated to scale and reposition all parts and objects by hand.

I was thinking of exporting everything scaling it and reimporting, but I loose file functionality on some modifiers, so that work around seems not a good way.

Thanks for your help!