[agrace]

Is a mutation an introduction of new genetic information or simply an alteration of existing data?

[balrog666]

Is a mutation an introduction of new genetic information or simply an alteration of existing data?

Yes, obviously.

[BMCDA]

That depends on the mutation. If the information carrier is extended (as happens during gene duplications) then you have more space for additional information.
If this doesn't happen, you have only alteration of already existing data. But if you change a piece of information you automatically have new information.