Thanks for the replies, mechanic mark and Moe Joe. I wound up taking off the left (chain case) fender and removing the chain case off the hex tube to replace both boots (like the video). All back together and working great!
Moe Joe, after pulling the chain case off the hex tube, I understand the Snapper service manual directions, and what you said. When I tried pulling the R. fender/differential/hex tube/axle off through the chain tube, it only moved maybe 1" at most, then wouldn't go any further. When I took off the L. fender and removed the chain case off the hex tube, it came off easy - no burrs. I'm thinking that the first try (Snapper way), maybe I had the differential/fender at an angle, and the hex tube was binding on the chain case. Also, when trying this was, I had the chain case in the park position - does it make a difference where the case is when trying to pull out the diff./tube/axle?
One last question, Moe Joe: I noticed the RH fender oil seal (outside of fender) is letting a little oil through. I didn't replace it, because the local Snapper dealer didn't have one in stock, and said the distributor warehouse didn't have one either - factory order! From looking at the seal, it appears there is a very small difference between the OD and ID of the seal. I've put a sheet metal screw in the seal housing before to remove it without having to remove the shaft its sealing, or use a punch on one side of the seal to raise up the other side to pry it out; this seal housing seems so narrow, I'm not sure if this will work here. Can it be easily removed without having to remove the differential housing?