First there is a utility to unpack stuff, it is just not distributed. But then, even changing offsets is altering the work!
For instance, when they decide to change quite a few german writing rules "new german spelling", authors forbid (and sued in at least one case) when the company did publish with corrected spelling. This only involved spaces in certain composita and capitilisation, so it was equivalent to the offsets.
The old paks were likely having a earlier makeobj version, i.e. all paks packed with that version (or a smaller version) are affected. That can be added to the program. This would require a bump of makeobj for vehicles for the sake of pak128, which we certainly can do.
But offsets are things which cannot be changed later without breaking stuff. If you decide to move tracks, you will break addons; not only cars, also bridges, tunnels and stations will be mismatched. I see no proper way out there.