I know that silver corners and such are easily added to most saddles by a saddle shop. A lot of times it's just a couple of holes and a rivet or chicago screw to hold the silver piece on.
Silver plates can be added to the cantle. I found a small silver cross that I hung on the breast collar D with a small piece of strong nylon string.
I suppose your imagination is the only thing that will limit you. You do want to be careful of the "bling" getting in the way of safety. I prefer to keep the embellishments limited to the small cross, shoo fly on the girth, and free edges of the saddle blanket/pad.
Sorry for the double post. IMO, If you want to add color and bling do it with the saddle pad, breast collar, and bridle. There are LOTS of pretties out there. You could even ride with rythm beads around the horse's neck if it will let you. There's ear bonnets, and browbands made of ribbon and sparklies, Pretty reins with embelishments on them etc, etc.
I just prefer to not monkey with the saddle itself.