Changing a saddle's billets...?

Having long girth points on your all purpose saddle will not affect the way the saddle fits nor how the horse performs. Dressage saddles have long points, as do some jumping saddles. My old stock saddle had long girth points.

You will need a shorter girth, and be aware that the horse may experience some chaffing from where the girth ends.

If you are having trouble doing the girth up, then yes, changing to dressage billets should be fine. You could try tightening the girth up at tight as you can then tightening it the rest of the way once in the saddle like Spify23 said in their comments, but if you don't have the strength to tighten it from the ground, then I am guessing you won't be strong enough to tighten it from the saddle, and if you did try it you have to make sure to have that girth tight enough so that the saddle won't slip when you go to mount.

Instead of changing them you can buy billet extenders which attach to your existing billets. This way you can 'test the waters' as to whether it would b a benefit before altering your saddle.

Also remember you will needs a shorter girth to compensate for the longer billets.

Have you also tried an elastic girth to help? Just be careful you don't over tighten it.

I really can't see how changing the billets would make a difference- it only allows you to do the girth up lower down nearer the horse's elbow. The horse may not like that and take a while to adjust.

Yes, changing the billet will make a big difference, varying from size(width/length), material. A billet with roller buckles should help you be able to tighten it better, and the shorter the billet the less you'll have to pull it, and different materials will help it stay in place on your horse.