-i dont think the psn network will mess anything up if you use it! but then again i have never used it.
-you can use the network update to update your cfw! just make sure your psp is set up properly before using! to do this go to your recovery menu, under configuration, and make sure where it says "use M33 network update" it says enabled!
(if your not sure how to get into recovery, you need to power off your psp by holding up on the power switch till it powers off....then hold in the R button when powering back up!)(or hit select while in the xmb and choose restart and hold the R button in after that!)
-dont mess with anything in the recovery menu if your unsure what it does..

just some friendly advice!