Unless you try some of the CIQ apps, you're locked into what Garmin has on your model of watch. You can change the activity later in Garmin Connect, but of course, that is not the same.
Then in that case looks like it is not currently possible on the Forerunner 45. In the Forerunner series it would just be for the 255, 265, 945 LTE, 955, and 965.
You can request it here - Share Ideas | Garmin, but It's probably not likely to happen on a watch that is more than a few years old.
