Upgrade to 6.4

Before I upgrade to the new 6.4 i would like to ask a question.

I have made some alterations to the original version I downloaded, not many but a few.

How easy is the process of dropping the new version into its place.

Will it revert back to a default stage?

I think what is really needed for those that do mod the application is a change log. Prehaps from v7 this could be a possbility.  Forgive me if one exists as I have not found it.