You don't want to go to 10%. Dyneema rigging is sized to get the right amount of creep, not strength. This results in larger diameter lines with breaking strengths way above shrouds made from
steel wire or rod. Cranking a dyneema
shroud up to 10% of its breaking strength may well break your
boat. I've done a lot of rig tuning for
offshore racing and I do not have a way to measure tension on dyneema shrouds. Just go sailing and tune it by feel.
Head out in a good stiff breeze and adjust until the
mast is where you want it on both tacks. A gauge is nice for repeatability, if you change things often and want to get back to where you had it previously, but it's not needed.
edit: I sort of mis-read your post. What I said stands, but as for re-seating after splicing, a measurement might be good. I don't know. I just tune 'em I don't make 'em.