If the pool deck is being replaced at this time then you should replace the plumbing. On older pools if you have one leak others are sure to follow and on some older pools the plumbing was not PVC. Its nice to have new return fitings to plaster around. Replacing your plumbing thru the pool wall will be a little tougher after you plaster and if you do go thru the wall you will have to drain the pool and replaster around the new fittings.