How (not to) add a Walk activity profile

TL;DR - this approach didn't work. But maybe it will save someone else the time if they avoid the experiment. ;)

I've been frustrated that the Garmin Forerunner series doesn't have a "Walk" activity profile, despite many requests over the years. My 735XT can do stand up paddling, but not walking? It boggles the mind.

(And please, don't lecture me about having "bought the wrong watch" - I bought the watch which matches the vast majority of the features I need and want, but this one is missing).

Anyway - when certain activities are enabled on the watch, we get various files in /GARMIN/SPORTS i.e.

0RRUN.FIT
10HIKE.FIT
12TRSTR.FIT
2CBIKE.FIT
4SOPEN_.FIT
5SPOOL_.FIT

one for each activity type. I can create a "custom" activity type on the watch, and name it "Walk" - then I get:

11GWALK.FIT

If we look at this file, it's a "Sport Settings" file as described in the ANT+ FIT file SDK. It contains the activity name, and activity type; when created on the watch, the activity type is generic:

Local message type: 3 (message name: sport, message number: 12)
sport (0-1-ENUM): generic (0)
sub_sport (1-1-ENUM): generic (0)

I modified the sport number to make it "walk" instead of generic:

Local message type: 3 (message name: sport, message number: 12)
sport (0-1-ENUM): walking (11)
sub_sport (1-1-ENUM): generic (0)

and updated the CRC to make everything copacetic, and copied it onto the watch, and ... no dice. The watch says "updating" and upon further review, the old 11GWALK.FIT file is back in place. :(