what it means is, if the mainline snaps, can the rig slide off the mainline, this is in case a fish is towing line and lead around as this could lead to a fish getting tethered and dying.
I used to put a bit of 8lb braid (soft uncoated) through the rig ring, tie a knot in the ends to form a loop the right length for the bait then add a bait stop after pulling the braid through the bait
in some situations lead core would be okay, but i suggest reading this sticky post http://www.carp.com/carp-forum/viewtopic.php?t=53599
also use the search function to find lots of posts on chod rigs
A lot of anglers on here dont have a lot of time for leadcore, so you might not get much response to this as leadcore can and often is a potential death rig.
I have deleted your duplicate post, hope you dont mind
you will find the fuji seats are bonded to the blank, measure first but you might be able to hacksaw the blank both sides of the seat, cut blank but section to length then slip the fuji with section of blank over new but section
Has any one on here fished Gweryd Lakes in north wales, is it any good and do they have showers on site, thinking about having a 3 night session and taking my lovely lass with me