Relation of U-Joints and 4WD

No it wont keep it from 4wd operation unless it is snapped in two, butv it will damage the axle shaft to the point it won't accept a new joint. It is not a hard job, just remove brake caliper and rotor and axle nut, then 3 - 4 (don't remember) bolts on back side of steering knuckle, that hold unitized wheel bearing/hub on, remove bearing and pull out axle and repl. U-joint, re-install, 1-2 hrs. Total. Tje bearing may need some persuasion to get out of knuckle(hammer and cold chisel, between bearing and knuckle). Ok good luck. Let me know how it goes.