How can I make Drupal use token for summary instead of breaking at ? I'm using "Long text with summary" fields for some different content types.

Right now the summaries are rendered until the first -tag (the web site already contains ~5000 nodes) but I would like to use a token created by a module that I'm currently using for the meta description of each page.

How can I use a token to display a nodes summary in a standard taxonomy node listing?
Assuming you're using Drupal 7, you can change how the content type is displayed in 'manage display'. You need to make sure you are using the correct view mode (probably teaser) which can be selected in the top left. You can then set the format to 'Summary or trimmed' and adjust the trim length by clicking the cog button.