"James M. Knox" wrote in message ...

Legally the transponder is the only one you can NOT do this to. The entire
*system* is suppose to be certified together. '

In addition to the certification issue, the transponder is excluded from the
owner maintenance.

But that's just "some pilots." Seriously, the correct thing to do is to
have a shop do stick it in and do the certification, with appropriate
logbook entry. Will cost about $200.

The transponder itself will probably only run half of that...unless you
managed to muck with the encoder or the static system in the process.