UKH

Has anyone added extra straps to a rucksack or is it too much faff? 

I've got a DMM Short Haul which is great, but I can't help thinking it would be even better if it had the rope attachment and internal compression straps of the larger DMM Flight. I have a sewing machine - assume would involve picking the seam and then sewing the straps in. 

I have done extensive mods to packs. Using glue/seam sealer and stitching.

You must have a chunky sewing machine.  I have just used hand sewing, or a Speedy Stitcher (like an awl) with conventional strong nylon thread (not the waxed string the Stitcher comes with).

It's hard work, so you have to WANT to do it.

I think it is worth the effort.  A lot of my kit is modified and it is very satisfying to use something you have improved yourself.

Go for it.