Getting at individual links in mytheme_preprocess_node

I'm trying to edit the list of links that appear at the end of each node by doing...

function mytheme_preprocess_node( &$vars )...

However the contents of $vars['links'] is a string of all the links rendered down to HTML.

Is there anywhere else I can tap into the preprocessing chain to get at these links while they are still individually addressable?

Cheers,

Roger.