dvd's are usually cheap enough and your time and labor dear enough that you should just buy another copy rather than do this.
plus, the dvd/cd may be obsolete in 5 years so why bother.
Well, ok!
Not all titles are replaceable.
If you acquire a library of movies over time (say 5-20 years, VHS, LD, DVD), you will find that some titles go out of print altogether, whereas others are rereleased in alternate edited form (you cannot buy the theatrically released version of Blade Runner on DVD), and some are reissued without commentary tracks or with different/lesser supplements.
But if you keep fingerprints off of the surface area and don't stack up discs so that they can get scratched, they should last a good long time (at least until rot sets in).