This may have been discussed on here but my search revealed nothing so I figured I'd post my experience. In general BB are not cost effective or worth rebuilding but in a pinch this may get you down the road. And this is not really a rebuild so much as it is a cleaning and regreasing. The model I took apart was a CS11, very similar to the un54.
1. Find a clean place and work on a towel or old shirt so the bearing don't hit the floor and scatter. Remove the BB.
2. The non-drive side will have 2 seals a hard plastic and a rubber seal. Being very careful a sharp tool like an awl can be used to pry those out. The drive side will have one rubber seal remove the same way.
3. There is a lock nut, spacer, and a cone nut in that order on the non-drive side ALL LEFT HANDED THREADS. Not sure of the metric size of the lock nut as nothing metric I had would fit it, but a 13/16 sparkplug socket fit it fine. Hold the axle with a 14mm wrench and remove the locknut and spacer. The cone nut must take a very thin tool to remove, no way you'll ever get a normal socket in there. But, using a flat bladed screwdriver wedge it between the BB wall and nut flat and turn the axle with a wrench to remove. The cone nut is not on there tight so it doesn't take much to remove.
4. The bearing sizings are different between the sides so keep them separate and remember where they came from.
5. Remove the bearings and axle and clean everything. Pack new grease in the BB.
6. Insert the axle from in from right to left leaving it hanging out just enough to get the bearings in the axle groove. Once the bearing are in slide the axle all the way in. At this point you will have to hold the axle in place. If if comes out the bearing will also fall out.
7. Flip the BB and insert the bearings in the other side.
8. Screw on the cone nut. You can hold it well enough with your fingers to spin the axle and screw the nut on well enough to hold the bearings in place.
9. This next step is just kind of a feel thing that you will have to play with to get the proper bearing tension. Place the spacer and lock nut on and tighten. As you tighten the lock nut it may also tighten the cone nut to much. I found that if I placed the cone nut on just slightly to tight, then screwed the locknut down with just a socket turned by hand. I then held the cone nut with the screwdriver and turned the axle to back the conenut out into the locknut that I got the proper tension easier.
10. Pack a bit more grease in the outer part of the BB and reinstall the seals.
Overall this took me about an hour to do. The results were quite good as it does feel like a new bottom bracket but I don't know yet that I would trust it any distance from home for very long, but it will get you until payday, or until the new one arrives for sure. And I'll keep it as a spare when the new one gets here. I live 60 miles from the closest LBS so everything has to be ordered unless I want to make a trip and waste gas money.