"Available Updates" behavior

Lets say I make an edit to links/admin/Links/User/Review.pm

I change:
$input->{Review_Validated} = 'No';
To:
$input->{Review_Validated} = 'Yes';

General questions:
How does the updater deal with my customizations? Just overwrite them?
How do I know if an Official update overwrites this customization?

Is it possible to have a "custom update" that would be shown on the Available Updates section of the Admin?

This "custom update" could apply edits I have made to the source code. I would "install" the custom updates AFTER doing an official update. Just an idea.

Thanks
Chris
RGB World, Inc. - Software & Web Development.
rgbworld.com