Not at this time. You can create as many custom-named workouts in the Other category, but you cannot create a new category.
To create Yard Work as a named Other workout, follow these steps:
1) Open Workout app and locate the Other category but don't tap it.
2) Tap the three dot More button at the right side.
3) Choose Create Workout.
4) Select Custom.
5) Tap the Add button and select Work and then choose Open or Time.
6) Scroll down and give it the custom title of "Yard Work."
7) Press Create Workout
You then have an Other workout with the name Yard Work, which you can tap to use and reuse.
Repeat the steps for House Work and any other workout you want. Once created, just tap on the workout you created and do your thing!