The airbag control module (also called ORC - Occupant Restraint
Controller - located right of drivers right foot - on the side of the
hump behind the console cladding is where the firmware resides) firmware
is where this improvement resides.  If they didn't change the connector,
then I would think the earlier and later modules are interchangeable,
and the improvements could be effected by simply swapping out the
original module with a later one.

It could be that the dealers show the older module part numbers
superceded by the later ones.  If you find that to be the case, then
that would confirm that it's a matter of swapping in a later one.
Here's the P/N for the '99 ORC: 4602350AC - see if it's superceded by a
later number

(For reference, '03 and '04 P/N is 4602406AC; '00 thru '02 is 4602430AF)

It may be that they would obsolete the old ones and replace with new
(that they would be interchangeable) - but there's no guarantee of that.

Maybe Glenn knows the answer or can research it.

If you do find that the modules are interchangeable, you should be able
to find airbag control modules by whatever year you want on
www.car-partcom for under $50.

The above is provided for reference and needs to be verified - it is up
to you to find the correct information before making any changes.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')