I think I'm missing the point here, so let me give examples.
PrusaSlicer (not any client) doesn't need anything changing, we use the same interface as now, the same words.
1. When the user selects "Upload", it goes to the group selected in the Repetier-Server dialogue box - No change.
2. When the user selects "Upload and Print" AND any group but "Default" is selected, then the file is sent to the Repetier-Server print queue, as now, but is also copied to the selected group in Repetier-Server. The new behaviour is the copy from the Repetier-Server print queue, but since you control the server and you already have the functionality, this shouldn't be that complicatated. I assume there's a directory system and/or a database, e.g. SQLite.
3. When the user selects "Upload and Print" AND the "Default" group is selected, then the file is sent to the Repetier-Server print queue - No change
4. Every file printed is automatically sent to a Group called "History" which is a new Group that exists for each printer which is a simple time ordered list of what has been printed. - This is basically the same as point 2 but to a specific Group.
The changes are copying a file from the print queue to a specific Group. That's it.
Thanks
Rob