Waypoint 2's location is not changed by doing it with the method I described. (just tested! heh)
With UTM you can press the ?3* button first to create the waypoint, then press the bottom left OSB to copy the scratch pad into the current waypoint, which is what you're describing. Or you can type in the scratch pad first, then click ?3* to create a new waypoint 3 with the data from the scratch pad.
With L/L the bottom left OSB (the unlabeled "copy scratchpad into waypoint" button) is used for the EAST coordinate, so you can't make it first then copy into it like you can with UTM. At least I couldn't see how. hehe