Bulk edit activity name

Maybe just add a note when the change occurred, to last activity or the calendar.

Other options:

• depending on a file type, use a text editor and multi-replace names in files from a directory, before import,
• write a script - below the request to change an activity's name.

fetch('https://connect.garmin.com/modern/proxy/activity-service/activity/' + act.activityId,
{
    'headers': { 'Content-Type': 'application/json', 'NK': 'NT', 'X-HTTP-Method-Override': 'PUT' },
    'body': '{"activityName":"NAME","activityId":' + act.activityId + '}',
    'method': 'POST'
})

If I were going to script this, I would do it in 4 parts (assuming the names of the runs to import can’t be edited somehow before importing them.)

1) Use a script to add a suffix to every existing Garmin Connect activity name which will never occur in any real data (something like “ [ORIGINAL]”)

2) Import all TomTom data to Connect (hopefully the runs can be bulk imported)

3) Use another script to add another suffix to all activities which lack the step 1 suffix, like “ [TOMTOM]”

4 Finally, use a script to remove the step 1 suffix from all activities

I have no idea how importing from TomTom works though. Do you get individual FIT/GPX files and do you have to import them one at a time?

Another possibility, if you want to limit the scripting, or when you want to avoid it completely:

1. Change the Activity Name naming pattern to "Untitled" in GC User Settings
2. Import the files 
3. Now all the new imported files are titled "Untitled", which you can easily filter out in Garmin Connect, and change in bulk either by a script or manually (which is possible in GC Web directly on the Activity list page, without the need to enter the activity details, hence rather quick).