Is it currently possible to change the peer_id which Tixati reports?  I ask this because my favorite private torrent site uses a torrent client white list, however Tixati isn't on it (and they RARELY update it (only bad thing about the site!!!), for example the last uTorrent version they approved and added is from 16 months ago...).

If it's not possible now, could this be added as a setting?

Assuming Tixati is a proper client in terms of tracker reporting (which is the point of the white list, to reduce ratio cheating by using bad clients), then this seems fairly harmless :)

go to peers section.

Read this topic: http://forum.tixati.com/support/456/

From the News page:
In tracker URLs, a :header: directive may be added to the end, followed by URL-encoded HTTP header line(s) that are to be used in place of the regular UserAgent line.  A :peerid: directive may also be used on the very end of a tracker URL (after :header: directive, if present) to override the peerid parameter for a single tracker.