Replacing a single damaged S300 shaft with a new S300 shaft is a lot different than reshafting a set of 3-PW from S300 to NS Pro 950.
If you're replacing a damaged shaft with a like shaft, it would be fairly simple to do.
If you're reshafting an entire set with a new shaft, you need a swingweight machine, tip weights to recapture swingweight, a sharp cutting saw to tip-trim (if using parallel tip shafts) the shafts before installation, and butt trim to length after shaft is epoxied to the head.
Reshafting isn't hard if you know what you're doing. If you haven't done so before, you might want to practice on a bargain barrel 5-iron before you do it on your good set. Be aware that garageland reshafting likely will void any warranty on the clubs.
Regripping is simple - if you know what you're doing.
You also need to get the equipment, and have workspace/processing space to do it. And, you need some quiet time and patience so you can do a quality job.
If you know a local clubsmith, you might ask him or her if you could observe reshafting sometime on a quiet day.
If you really want to learn how, you could attend one of the GolfWorks clubmaking academy basic courses. Check out the website: http://www.golfworks.com/article.asp_Q_ai_E_494