Thanks for the quick reply!
After posting my request yesterday, I couldnt stop thinking about the whole cargo loading/unloading issue. It keeps me the half night from sleep and things got worse, the longer I thought about..
Probably, my conclusions are of interest to you.
1. A change of this scale in the ecosystem would change the whole gameplay completely. So, is a "patchpack" the right place to alter the game completely or it's maybe wiser to do it in the openttd main trunk?
2. The patch, I posted yesterday does not the whole thing. It only makes possible to load/unload a specific cargo. It should be possible to load/unload a specific AMOUNT of cargo.
3. Concerning the GUI and the whole organization of the function it might be a good idea to introduce "suborders" where either the currently availible load/unload options are part of (the suborder list) or the suborder-list is referenced as a load/unload order. I hope you understand what i mean, sry for my english...
4. Refitting cargotypes could also be done as suborder, so manual refitting at a station is not limited to one cargo.
As of writing this, I will be not upset when you tell me that a change in such scale is too much work and if I want those features I may do them by myself..