Why don't you use the Midi configs i told about in my first reply? If you create multiple midi configs using midi learn, then afterwards you just select a midi configs with your mouse to change the mapping.
Keep in mind that a parameter can be controlled by 16 midi channels, but just one at a time. A midi confing can in example have aftertouch ch1 in one midi config and aftertouch ch2 in another.
I don't think the Midi CC work in OMNI mode. It would be great, if that was an option, so a Midi cc for a control would work no matter on which midi channel the message is sent. I think perhaps, i can remember years ago, that some old Arturia applications could do this. But i'm not 100% certain. I would vote for this feature. (I also would'nt mind, if one could write midi cc mappings in a file.)
If you have a controller or something else, that can send a OMNI message, then i can't tell if Arturias applications will react on this when midi learning and then set a parameter to OMNI. I don't have the possibility to test this.
A good thing about beeing able to use multiple midi channels for midi cc messages is that it can expand the number of availble midi cc's. (But when MIDI 2.0 arrive, then things may change a lot.)
Perhaps this method depend on the DAW, when used in a DAW.
Have you tried this?
Some controllers have controls that can be set to send on a certain midi channel. I don't know if any controllers can set aftertouch to a certain channel that's independent though. But if your controllers all can set a control to work on a certain same midi channel while the keys send on different midi channel, then this also is a solution.
Perhaps this method depend on the DAW, when used in a DAW.
Have you tried this?
When you say "assign by hand ...", then do you mean to be able to write the informations in the midi learn popup window by using your mouse and your computer keyboard? But how will you do this without being in midi learning mode?
If you don't mean normal midi learn, and don't mean changing the parameters values by using your mouse (Nothing to do with midi learn.), and don't mean using Midi configs, and don't mean the above writing in the midi learn popup, then i can't understand what else you mean. Where excactly will you change excactly what and how excactly will you do it?
If you wan't something, that you can't do now, then it's a feature request - yes. But then what excactly is the feature request? A MIDI OMNI mode for Arturias applications individual MIDI CC's?