I am going to reply to myself, as after reading most of this thread, Reserved upload slots for Subscribers?, think I understand something else…
“Strava sends me alerts (webhooks) every time someone saves an activity in Strava”
So does a Strava activity edit generate a new alert? Maybe only certain types of edits? Yes to activity type (“Sport” pulldown) no to “Shoes”?
If this is the case, I wouldn’t have to do anything. Start an “Other”, and change to “Walk” (in the app xor web). Will try as an experiment (when Strava backlog subsides).