If your firewall blocks you on 6346, only you should need to change your Gnutella client port to an available firewall port.
Everybody you connect to can be whatever they want, even 6346, as long as it works for them.

Example: You go through your port xxxx and into 6346 at the other end. The other end has nothing to do with your firewall settings.
There client will 'know' what port you are on!

I noticed however, that one or the other client have a small problem yet to be fixed, that if you change from 6346 to another port, there are upload problems, or something like that.
A small bug.

JD