I don't think it would be a problem having them change out a SS blade for a CV blade, as long as its a pattern they have them for...
Same goes for your old Case. As long as they have the right pieces, I'm sure they will work on it.. The blades won't be the same as the old ones, they will have current/recent tang stamps.
If the older one has nice red bone or green bone scales, keep in mind that anytime they disassemble a knife, there is a chance that the scales might crack or break. They don't have those anymore, so they would get replaced with scales of another material.