Square taper Shimano spindles are easily and quickly removed from sealed units, but they use integrated bearing assemblies and likely do not match the bearings on other kinds of bottom brackets. They are also exceedingly difficult to reassemble without some sort of jig and the seals usually are damaged during disassembly. If you are still curious about it, try disassembling the least costly one (likely a UN26, which has JIS tapers) as follows:

Remove the rubber shaft seals and the housing seals underneath them from both sides of the axle, prying them out using a hooked pointed tool like a stout dental pick. Remove the flexible nylon bearing retainer from both sides. Grasp and pull it with a small needle-nosed pliers or hemostat, or insert a hooked point under an edge directly to one of the balls and pry and pull upward until the retainer pops out.
Push all the bearings (7 on each side) around together to one side of the housing, to the same side on both ends. Snap the axle out of the resulting half-ring arrangements of the balls to the opposite side of the housing. Then push a single middle ball on each side inward out of its race grooves, thereby releasing the axle for removal.