I have an old Hermes that has cracked panels. I am wondering if I can have them replaced as opposed to recovered, hopefully to fit a larger horse? It perfectly usable right now, especially on the smaller horses, but seeing as I typically ride larger horses these days, I was thinking that if I have the leather replaced, why not go the whole hog and have them reshaped into a wider gullet? It is possible? How much would it cost if it was?
Ok I'll bite. Its probably not worth the money to have them replaced/recovered. MAJOR surgery on your older saddle..and what your left with is an old saddle, old tree, and old seat sitting on nice new expensive leather and padding. Murphy's Law says if you put a lot of money into it some thing else will break..and want fixin..more money spent..when you could just invest it in a newer saddle with more years life left.
If its useable as it-get it restuffed to fit yout big horse, buy a nice fluffy pad to hide the age and enjoy your saddle.
If you do this, get it done right by someone who will do beautiful work once and will do it in a saddle- and horse-appropriate way. There are some botched jobs out there and a bad repaneling job can make the gullet more narrow, not wider. I'm not sure if the saddle's skeletal structure will let you widen the gullet.
In any case, Bevals in New Canaan CT is the place that does quality saddle surgery that I know about. They will charge accordingly.
But the real reason to hesitate is your wanting this saddle fit on "bigger" horses. If you mean wider, it may not work. Hermes are narrow by modern standards and you can't modify the tree to the extent you might have in mind. Putting in thicker panels (as I suspect even appropriately thin ones would be) will not make this saddle fit.
If you are still gung-ho, do put the saddle on some of your string and see just how "too narrow" it is before you start.