is there a way to change activity category in a large batch?

SDF said:

Activity Type = Running

AT ID = 1

APT = 18

Yep, that's correct.

It's not super user-friendly or intuitive, but if you use --dry-run and specify a date range that covers an existing activity of the type you're interested in, the script will print out the type name, type id and parent type id. (So you can find out the type info for any activity you want by manually creating a dummy activity and using that procedure.)

worked with ptid = 17 which was what a correct run was logged with

Oh sorry, my bad. I assumed that my example in a previous comment was correct haha.

Thats cool, saved me over 800 manual updates, is there anyway to change the Subject "Uncategorized" to "Running" also?

It looks like "uncategorized" is:

type: "uncategorized"

typeID: 12

parentTypeId: 17

(Another way to discover this information is to use Garmin Connect Web to change the type of an existing activity, while the network console is open) (Press F12 in Chrome or Firefox)

So you should be able to use the command line options for filtering on an existing activity type, with the above information.

It should be enough to add the following options to the command line:

--match-activity-type uncategorized

As in the subject yes?  the running type is correct now.

Oh sorry, my bad again.

There currently isn't a way to do so with this script. If I find some spare time maybe I'll take a look at adding that functionality.

only small note:
Not sure if "uncategorized" is correct. When I imported something like hiking or any other sports than running or biking, all has activity type "other" not "uncategorized"

I meant when both the "main type" and "secondary type" are uncategorized, but good point.