Hi,
You'd hardly be the first person to apply LLA over existing lube. No need to remove the original stuff.
Everybody who uses LLA has his own favorite way to apply the stuff. Some do it "full strength" while others thin it w/ mineral spirits. For myself, I get a coffee cup full of boiling water, put the bottle in and let the stuff "melt" until it's quite thin. Then I put 25-50 bullets (depending on size) in a margarine tub, sprinkle a few drops over 'em, and swirl around a while until they are uniformly "dull" in appearance.
From there, they get dumped onto wax paper to dry. Some folks like to stand 'em up so any extra lube can run down toward the base. Once in a while I might do it that way, but not usually.
After they're dry (overnight usually does it for me), load and shoot a few to see if you got enough LLA on 'em to do the job. Some loads take two treatments...
And, once they're dried, if the bullets are likely to be used anywhere they could get blowing dirt or sand stuck to 'em, or they're going into a pocket where they can collect all manner of treasures, I wipe the loaded cartridges down w/ a rag and some mineral spirits. Same treatment goes for my auto cartridges even if they're going straight from the box to the magazine--the stuff CAN sometimes build up on feed ramps and the like, causing feeding problems.
Experiment a little... you may find it takes very little extra lube to work, or you may agree w/ a buddy who says "LLA good, more LLA better!" Or you may find happiness in between.
Rick C