Override already-declared function?

Hi folks, Is there a way to override a declared function? For example, if my site is running under a specific theme, I want function X to work in a slightly different way to normal. The theme will include a specific functions.<<themename>>.php file, which includes various function definitions and other cool theme-related stuff. I'd like to be able to redefine functions in these files. At the moment if I try it I just get the "already declared function" error. Any thoughts? Jason -- Jason Murray jasonm@melbourneit.com.au Web Design Team, Melbourne IT Fetch the comfy chair!