The files are already distinguished by their extension (.sldprt, .sldasm & .slddrw).
By prefixing the files as you suggest, you will lose the automatic "Open Drawing" functionality when right-clicking a part or assy.
Part numbers can be assigned when you add file to the vault.but not during a state change.
To Assign a serail to assing serial numbers to Files. Add a variable to File Data cards which takes default value from a serial number.