Club Obi Wan

My original strap is sewn onto itself on my gas mask bag. I assume I just cut it off and replace it with the leather strap?

Is the original strap used on any other props?

Just scissors, I store mine in my bag.

If you have 5 minutes and a seam picker (or thin ended sharp knife) easy to remove the stitching from the end that doesn't have the buckle. Feed the loose end through the buckle and remove strap. If the original strap is still in good condition them they do sell on ebay as spares for reenactors.