I don't know if this is general knowledge, but I couldn't find anything about it, so I came up with the following.
What you'll need- Cordless drill (variable speed is better)- 4 to 4-1/2" bolt (threads and head size don't matter)- A washer (or two) and nut to fit said bolt - An empty spool from line you've used.
1: Get the empty spool from some used line. Also grab the 4 inch bolt that is small enough to fit through the spool, a large washer (or two) and the nut for the bolt.
2: Put the bolt through the center hole (use a washer if needed on the top side, sometimes adding a lock washer helps) on the empty spool, slide a washer up the bottom side, use the nut to tighten it up.
3: Attach the spool/bolt rig to a cordless drill so it's good and snug. Take some tape and adhere the end of the line off of your reel to the spool, give it a few wraps around. Then, slowly at first, start to peel line off the reel with the drill. Forward or reverse will depend on what side of the reel you are comfortable with, doesn't really matter. You will have to slightly move the drill side to side (or use your finger if you can) to get the line to lay right. Try to get even and snug to the spool. I like to give myself about 8-10 feet between me and the reel in case it stops. Reel can be mounted or not to a rod. Should only take you a few minutes to completely un-spool your line, and it's back on a spool, ready to be used again!
There are a couple of situations where this can be used, if you have a few wind knots in braid, and you are getting close to your backing, but you think it's still enough braid to save, this will work. Maybe you'd just like to change your backing from a lighter to heavier mono... I personally have always changed my line from season to season, braid or mono, and this is how I do it.
Hope it helps somebody.
"There is no greater chapel in the world, than a man, alone, with a rod in hand and unlimited possibilities in the water before him"