On the Boris IV and Bertik IV Photo backpacks we changed the standard Fastex-type buckle on the waistbelt to the military-grade AustiAlpin GT Cobra Buckle. The design is radically different from the standard buckles. It is far more easy to operate (even one-handed), faster to open and virtually indestructible.
We offer this 38mm Polymer Cobra Buckle as a replacement/upgrade for your current buckle. It is the two sides adjustable version and it is not very hard to do the exchange.