I've had long straps exchanged for short straps on one of my dressage saddles, and I'm very tempted to have my other saddle done too. Just waiting for said horse to finish growing/filling out, so that I can be reasonably confident I won't need to sell his saddle any time soon. I do keep the removed long straps however, so they could just as easily be replaced.
Barrie Swain has stopped making saddles now, but his dressage saddles were made with long straps and are available second hand. Lovely saddles too. Well, TBF, I hate them but the horses love them, so that is that!
On some saddles, the full length of the strap is leather and you can just cut them shorter and punch more holes in them. I don't know which ones these days, maybe others can help.
Have you tried the horse with a girth fitted with the buckles right up to the bottom of the saddle flap, as is now recommended by the biomechanics experts?
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Not all girth straps can easily be replaced with short, some point straps are run under the knee block and then it gets really tricky. I would also recommend trying as long a short girth as possible if you're getting rubbing issues, or don't rule out the right WH saddle, you can even put leather loops on the stirrup bars to set the leathers back to dressage position. Some come with deeper seats and bigger blocks if this is your preference and fits both of you.
My horse objects to the girth buckles being lower than the flaps. I've had several dressage saddles and mono flap xc saddles and all make him grumpy. Since changing to a jump saddle with short straps he is fine.