At present, there's no way to edit the calories burned; however, you can tweak the activity to more accurately reflect what your HRM says. I would keep the time the same and tweak the speed for a relative number of minutes each
For example, when I used to play tennis, my HRM said I burned less than FitDay calculated, so I would enter, for an hour, 40 minutes singles tennis and 20 minutes doubles tennis. So possibly you could do 4.0 mph for X number of minutes and 4.5 for the remainder of the half hour, tweaking it till it balances out.
But I agree, it would be wonderful to customize an activity. That was in discussion for a while. Maybe someone will let us know if it's still an option on the table.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days