When loading a airport scenery (like KSFO-HD by FlightBeam) that already use SODE, I cannot modified the Jetway parameter using the Parking customization page. Is this normal?
Yes, this is the intended behavior. You cannot normally edit SODE jetways in 3rd party airports. Not automatically. There IS a way, if you really want to do that, and is to remove the XML file for that airport here:
C:\ProgramData\12bPilot\SODE\xml
But you should be VERY careful, since the scenery might use SODE for other things too so, ideally, instead of removing the whole file, you should remove only the Jetway sections from it.