you can do it!
if you're a better-than-average home mechanic, you can do the shock if you have some good professional guidance first time around. once you've done it..., you'll see that it's not really all that big a deal, and you'll know what questions to ask before digging in. it's messy..., but not technically difficult.
i've done a couple now. it takes me awhile..., but i like being secure that all the all the old oil is gone, all the parts are squeeky clean before reassembly, there's absolutely no air in the system, and any worn parts have been properly replace. i suspect that sometimes, that much care just isn't exercised at a "time-is-money" shop (and you can betcherboots that for a shop to make money..., production time IS an issue).
if you have a shop that'll let you sit in the maintenance bays & watch..., take the time to watch them do somebody else's shock.
and read your shop manual, carefully
you might end up having somebody do it for you, anyway.
i would definitely echo gary b's suggestion (at least partly), that you take it to a shop for the nitrogen. it's $20 well spent for not "blowing it" yourself.
whatever you do..., don't fly at it without some competent guidance. there's a couple of parts that you could break real easy. and if you break them.., it's purchase-a-new-shock time.
and one other thing..., if you're thinking about doing something to change the shock's damping characteristics..., disregard all that crap i just spewed at you, and take it to somebody who really knows what it's all about.
