I just bought a USP45 in varaint one(I'm a lefty), I don't know for sure but I think the change over to the other variants is done at the dealer level. That said the control lever is a $40 dollar part , I received instructions to change it over, but they suggest a HK Armourer. The LEM is another varaint that requires the LEM trigger group, this I am told is definitly a Armouers job. Hope this helps. Check out HKPRO for all the answers to your questions. BTW I switched from the SIG P220 to the USP, I needed a "double stack" since I have big hands.