Same happened to me on my kicker line in the middle of a race. I did a quick knot repair and carried on.
Then I followed the Youtube links here and others I found. (I find myself hearing "Rooster Easysplice Continuous Control Line" in my sleep now
)
So I bought from Sailboats.co.uk
* a pull fid and a couple of small fids as a 3 pack (£19.95)
* 3 m of 4mm dyneema to practice on (£3.54)
* a roll of Marlow #4 whipping twine (£5.19)
From Ebay I bought a pair of CK Tools Heavy Duty Electricians Scissors for £13.60 (the middle set in Pete's review which worked fine)
After a bit of experimentation and Youtubing I worked out that it was easiest if I covered the cut end I was pulling with sellotape leaving half an inch spare to flatten at the end. I could then fold this flattened sellotape round the end of the pull fid and it helped the rope get through the hole without coming loose. I also used one of the small fids to help enlarge the entry hole a little. I then found that in order not to lose the rope half way down it was best to "milk" the outer braid over as well as pulling gently.
After a couple of attempts I got a good secure splice and tacked it with the twine (which went through with an ordinary needle very easily). Rock solid.
So I went to the boat this weekend and did a reasonable splice before realising that, working without having the boom and kicker up, I had inadvertently fed the line through the kicker shackle when doing my mid race knot repair.
(Schoolboy error - some bad language ensued). Check your lines are fed right BEFORE SPLICING people!!!
As I had tacked the splice with twine I found it impossible to undo without damaging the braid so I had to cut it and resplice. There seems to be a fair amount of spare with the boom down and the kicker slack but once rigged it turned out to be a close thing so don't do get too enthusiastic with your splice lengths without checking with the boom up and kicker attached! Anyhow the second splice was neater than the first and held in some quite breezy sailing over the weekend. Result!
So as somebody who can hardly sew a button, has no spatial awareness that my wife can discern, and has never done anything like that before I was pretty chuffed, and would say if I can do it anybody probably can!
It cost me about £40 but I'm ready for next time now!