Afaik, the current library format doesn't allow that (yet).
There is only one field for those values with positions per part. The different sub-parts are differentiated in a 'DRAW' section of the symbol definition..
Quite possible that this will change in future once EEschema is refuirbished.. months/year away.
Afaik no, probably in (far) future.
The format only knows sub-parts by having elements in the draw sections that have a different number at an index position.
For single parts all drawing elements have a '1' at that place.
For multi parts '1' equals 'A' and '2' is 'B' and so on..