you can do quite a bit by yourself if you have a little time and a few basics.
i change my grips to suit my taste for each bow - lay down a little scotch tape wrapped around the grip sticky side out and use some modeling clay that i get at a local arts and crafts store.
shape to my likings and let it dry for a day or two, cover with a rubber grip or leather - works great
here's a pic or two from a couple of my old bows -
thumb area and palm swell on a widow -

finger grooves on a long bow and a build up of the palm area to change the wrist angle -

grip build

all sorts of things you can do. don't build right on the bowgrip area - lay down something underneath so it can be removed.
i usually use two strips of two sided scotch tape - one on the belly of the grip and the other on the back,
then wind scotch tape, sticky side out around the grip area.
after i get the grip the way i want, then remove the excess tape.
the whole grip can be later removed if you decide to sell the bow - like i did with both of these.