This stuff is injected into the existing wood with needles, and no extraction or removal of any wood is necessary. We use it here in Florida on boats all the time. It's simple to use, and makes a rock-hard, rot impervious repair.
"True eloquence consists in saying all that is necessary, and only that which is."
François Duc de La Rochefoucauld
The problem with this, is that the metal skin is incorporated into the wood frame through bending it into a profile. Removing the wood sets the metal free from the profile. You could remove the rotted perimeter wood. Route a similiar profile and dropping them in place. Apply construction adhesive to mate with the old wood. You will need to remove some of the foam insulation core to get the pieces in the frame. After the adhesive sets, drill a hole in the botton and shoot in some slow expanding foam to take the place of the foam you removed. Clamp all the sides until the foam has cured.
Prime and paint.