No need to go through customs or immigration if you are arriving from non-EU country and going to another non-EU country. Which airline are you flying? You mentioned Skyteam so I assume you are flying NW or DL? You would arrive in Terminal 2 and there is a nice DL lounge there that has a shower.

Just be sure you don't follow the crowds to passport control and luggage claim. When I did a similar thing (actually just wanted a shower before exiting the FRA airport) I went up the stairs just before the passport control which led to the departure level, lounges, shops, etc.

John