well, BITD i used jonnisnot to lube them, it is a grease that does not attack the plastics, and was the officially reccomended stuff. not sure if its still available, though google seems to suggest finish line and others produce the similar appropriate grease for gripshifters.
cables replacing is kind of straight forward, you undo the cover that is held on by a single phillips head screw, and slide the twisting lever off the main body. the cable once inserted into the retention and threaded out through the barrel, needs to have a loop introduced to it, and then set into the groove of the shifter. hard to explain in words.
mentally think of twisting the cable between your thumb and forefinger, so it loops over itself once. you then set it in the groove.
push the body back on the mounting, and put the cover plate back on and do the screw up.
terrible shifters though.i loathed them with a passion, and went back to rapidfire quick smart