Looked at my bar and tried to remember how i did it. You may want to drop Best Support an email just to verify.
1. Remove the leash ring from the end of the redline bungee.
2. Tie a length of old kite line on the redline end with a double overhand knot.
3. Pull through release, swivel, depower stopper and depower strap d-rings.
4. Untie knot from step 2.
5. Undo redline from front line. You should be able to now remove the stopper ball. Remove exsisting front flagging line.
6. Thread new front flagging line through ring. Put stopper ball on new front flagging line. Larger diameter hole toward bar.
7. Reattach redline bungee.
8. Retie old kite line to redline and pull back through to the bottom of release. It should go through d-rings, stopper, swivel than release.
9. Reattach leash ring.
The upgrade for the 2013 includes a new release and swivel. There were parts that were cracking so the redesign was to rectify these issues.
I dont think you can get shorter lines from Best than 20s. You may want to check with them. I suppose you can use other linesets but you will need to remove the other stopper on the kite end of he front flagging line and reattach to new ones.
I hope i explained it clearly enough. Good luck. It wasnt as hard as I thought.