Might not be applicable but .... When I worked in The Ski biz the chairlift haul ropes had to be spliced end to end w out any diameter gain at all. To do so there's a handful of companies that literally travel the world doing the "Long Splice" ... every haul rope has two , one at the time of installation and one more a year later after initial stretch and wear. Achieved by tucking the wraps way back on both ends and removing one third of the strands on said ends. You can't tell where they are by diameter.
I'm not sure you can do full strength end splice on double braid.... might need to get a new rope. I think ther splices that exist are for when you are at sea and you break a halyard or something, so you can get home. I don't think they are rated.
Any of the end to end instructions by the larger rope manufacturers, like Yale, Samson, NER, and others, will be rated from 90%-100% of rope strength, if done correctly. If done on used rope, the splice will be the same percentages, but only of the break strength of how much strength it presently has.