Small adaptations to existing modules

Hi all,

I have just started developing in Drupal and was wondering the following: Is there a way I can redefine some methods of an existing module without having to redo all the work manually when I install a new update of the module?
In fact I would like to be able to define the methods in a separate file and have them called instead of the default methods defined in the module itself... This way I wouldn't change the original files of the module but I would be able to override some methods.

In my case I have redefined the methods: translation_block and translation_get_links to display the links to the translations as a dropdown box instead of the default text and icon links.

Thanks!

Koen