Replacing the pendant line underwater may be the safest option for you unless you want to have a crane lift your boat. I've always been able to take my 222 off the trailer to do bottom paint and work on the centerboard when I had to, but I have sailboats stands, 6"X6"s and jacks. It can be kind of dangerous.
The O'Day 222, 192, 240, and the later model 25's and 26s have this sheave up inside the centerboard slot in the keel for the pendant line to ride through, but I don't think that your O'Day 22 has one. I could be wrong about this. If your pendant line pipe goes straight down from the cockpit to the centerboard, it probably doesn't have the sheave.
If you can get a diver you may want to have him go under and look at the pendant line connection on the board and let him decide if he can connect the new pendant line to the board under water. If he can, just take a strong string and tie it to the end of the old pendant line in the cockpit and have him pull the pendant line out through the bottom of the keel slot. Allow plenty of string so that you can tie the new pendant line on the end of the string from in the cockpit after he gives you the end. Then all you have to do is pull the new pendant line up into the cockpit and have the diver connect the shackle to the centerboard and you'll be back in business. If there is a sheave up inside your keel slot, you won't need to worry about it provided the old pendant was riding through it previously. I really don't think your boat has one though. Good luck!
Joe