This job can be a pain or a pretty easy job. The difference is all in the quality of the tools you use and your preparation. Done well, this modification does not look like a hack and works brilliantly.
Tool List: Safety glasses, lights, Dremel, wire wheel, paste flux, flux brush, wire cutters, soldering gun and one hand wire stripper.
Pull the playfield out and place on bench or rotisserie, or at least lean it back against the head. Set up some good bright lights.
You can do a handful of sockets all in the same area, to minimize picking up/ putting down the tools.
PUT ON SAFETY GLASSES!
Dremel w/ wire wheel: clean a spot low down on the barrel and the adjacent area on the bracket. Takes 5 seconds or less. You don't have to be too careful here.
Dremel w/ wire wheel to clean the 'tit' on the bottom of the barrel. About 2 seconds. Do both areas on about 5 sockets.
Put down the Dremel.
Brush a near invisible layer of paste flux on the cleaned spots on the barrels and bracket, and on the center connection 'tits'. Basically, get a fluxing brush loaded w/ flux (the brush will still look pretty much dry) and you only need to reload the flux brush every 10-20 sockets or so. A little excess flux is not an issue, just looks sloppy. Fluxing a socket barrel and tit takes 5 seconds a socket or less.
Snip off wires at lug on each socket, then strip the wires. This is the slowest part of the job. Get a good, one hand 'squeeze the handles type' stripper. You will never regret this, and never strip a wire any other way again. You will think you are a genius and you will annoy all your friends and family talking about your wire stripper. Maybe the best pinball tool ever. (Non-corrosive paste flux is a close second. Get it, use it, enjoy life without solder problems. Think you can't solder? You haven't used paste flux.) If the stripped wires are copper colored, not silver colored, then you must pre-tin the bare wire. Flux the stripped wire, heat it with gun and flow on a bit of solder.
Fire up your soldering gun. Not an iron like for board work, the big Weller gun. No gun? Stop, go to the store, purchase gun.
Grab the 60/40 rosin core 1/16" dia solder.
Pull trigger and wait to get tip hot on gun, then touch the gun tip to the bracket and barrel AT THE SAME TIME in the area you cleaned and fluxed. Allow them to get hot. Flux melts. Maybe 5 seconds, probably less.
Touch solder to barrel/bracket fluxed area, NOT the gun tip. Solder should melt instantly, if it does not, you are not heating the parts long enough. Bridge the barrel to the bracket with solder. The flux will do the work; when you do it right it's like the solder has a brain and knows where to go. Will look way better than the picture above. Do all the prepped sockets.
Melt some solder on the tip of the gun, put the solder down, grab a wire and 'tack solder' the wire to the tit. This move takes some practice. Do all the prepped sockets. When you get good, you can grab the wire with a couple of fingers and solder it without putting down the solder. Or put the roll of solder down with the end of the solder sticking up, so you can touch the gun tip to it.
THE TRICK: Do not release the trigger of the gun after you start- just move from socket to socket, bam, bam, bam. Once you get the rhythm, you will move like lightning. Remember to stand up and stretch your back once in a while.
Hate soldering? Freshly brushed metal, flux and the proper heat act together like a miracle. If you are having problems: more flux, more heat. You will figure it out. If you are not going to wire brush, flux and use a gun, DON'T EVEN START.
Cleaning the inside of the socket is your option. I do it with the Dremel, it's super fast with a tiny cup-shaped wire wheel.
Only buy the best possible tools. Compromise on wives, friends, food, booze, religion, politics and condoms BUT NEVER ON TOOLS. Can't make up your mind? Follow this simple rule - Buy the better tool. This is how you make working on pins very fun, and never a chore.