I've got some old 10.5mm/11mm climbing rope here (condemned rope because no history for it), which we use a 2m length of as a camp lead for the dog.
Things to think about:
- Proper climbing rope (dynamic) is actually quite solid, static (abseil) is even more so. If it can fold back on itself and not leave an eye at the top, it's knackered and the core is broken down. Static rope is like a wooden stick at times....
- Climbing lanyards are normally sewn rather than crimped - the stitching provides a visual cue that there is a fault with it.
- The "climbing rope" leads that you can get are basically a hollow core rope with a sheath around it, whereas a climbing rope is multi-stranded rope intertwined - these might crimp differently.
You can find instructions on line of how to splice climbing rope (normally via an arborist's site) but in the climbing world, it's not done that often.
Hope that all helps,
Ed