you do not
NEED to remove the seal and inner bearing from the hub to replace the rotors. you do need to remove the hub, and reset the bearing play, etc...so I guess you do need to touch that outer one....
but as I said earlier, and most anyone that has done the job before knows, you should repack the bearings at this point. the only exception would be if you had freshly packed bearings, and ruined a rotor shortly thereafter. then MAY-be one could get away without doing a full repack. ( I would clean and pack them , but some peeps live on the edge...)
but I also stated earlier- for the peeps whom do not always read every post- it is a good idea to keep extra seals on hand, so that anytime you get to this point, there is no reason NOT to clean and pack the bearings.
And as BC stated- all old grease should be removed, bearings inspected for discoloration and wear, then repacked with good DISC brake rated grease.
most flaps will have the seal on hand. and the bearing sets are #3 outer and #5 inner.