If you are going to replace any buckles then this may help
Quick Fix
If your buckle broke, and it was sewn directly onto to your pack, try this trick to replace it.
Required Equipment: Replacement buckle the same size as the original.
You can borrow a non-essential buckle from another strap on your pack.
Nail file, pocket knife (saw blade), or lighter.
Examine the broken buckle to find the thin plastic bar that the webbing is looped over.
Carefully cut, melt, or snip, a one or two-millimetre gap in the centre of the same bar on the replacement buckle.
Quick Attach buckles already have a small gap in the bar, and do not need to be cut.
Wiggle the nylon loop through the gap in the bar until the buckle is attached to the webbing.
I have used this process many a time to repair other peoples kit, gets better with practice and saves on somy very difficult sewing.