This is a PLCE Bergen I modified in 2010 everything is still working fine!
i added extra clips so up to 4 sidepouches could be attatched not because I want to hurt my back,but it allows the pouches to be carried in the middle back rather than the sides.I can't think why, perhaps if walking through woods with narrow gaps, or if you wanted to use the side straps to carry tools of some sort.
an extendable lid was also simply added by adding straps. This is probably the easiest mod, as it only involves cutting off the lid and adding the required straps and buckles.
I really wanted to modify the back and shoulder strap area wider softer straps and more supportive waist strap, but still can't figure out how to without seriously changing the design of the back and potentially damadging the bag (or my back) forever, but even so I'd need a more industrial sewing machine, doing it by hand would take hours...if not days!
I've updated the top pouch it now has clips and loops so it can be used with the side pouch yoke.
http://www.bushcraftuk.com/forum/showthread.php?t=51433