Yes, you can manually take away stars from a profile by adding a negative dash in front of the number of stars you would like to remove.
Step 1: Click on the Reward Tile
Step 2: Select "Give Stars"
Step 3: Enter the amount of stars you'd like to take away with a dash in front of the number
Step 4: Select the profiles you'd like to take stars from
Step 5: Review the "before" and "after" amounts and select "confirm"