how do you replace the water jets, also can i replace the "O" rings in stead of the whole jet?

it all depends on the jets and the tub... if you have a lot of insulation, that will need to be removed from around the jet. Some jets are glued in and need to be cut out. Most jets use gaskets, not o rings.

I'm looking to install approx: 10 additional jets into a 1999 Blue ridge spa to improve my tubbing experience. Has anyone ever installed additional jets and if so, what tools did you use and what proceedure did you follow?
Hey "hot tub addict, MN" i'd like to hear your imput!

Once you remove the insulation around the area where you will be installing the jet, you will need to take a holesaw and use it to cut through the shell of the hot tub. I would suggest start the hole from the rear, then as soon as the pilot bit breaks through, move to the inside and finish your hole there. You won't risk splintering the sealing surface that way. Choose your locations wisely, meaning choose the flattest surface possible to cut your jets in. Plumbing is pretty straight forward. You will want to have your air induction to each jet too most likely, and that would mean adding more air orifices in the tub as well. Lastly, you will need to add an additional pump or two. A general rule of thumb for sizing is 1/4 HP for every jet. A 4 horse motor can run 16 jets. To feed the motor, add another drain if you are connecting to the existing plumbing, but better yet is to add 2 drains and keep the new jet plumbing separate from the existing. When placing the drains, keep them as far apart as possible, and make sure you have TWO!