Updating an application for a faculty position I would like to ask if it is appropriate to update documents (e.g. cover letter) in the application package for a faculty position.

Thank you very much for your response 

Kind regards,
Yannis
I assume you're talking about making updates to your application materials after they have been submitted.  If you applied using a website that has a built-in facility for updates, then sure, go ahead.  It might not help (someone who already read an earlier version may never notice the update, or they might not bother to read updates received after the application deadline), but a few reasonable updates won't hurt your chances.

On the other hand, you should be wary of making updates if they aren't handled automatically, for example if you have to send an e-mail.  If a staff member has to update your file, you should be respectful of their time and avoid submitting any unnecessary updates.  A nontrivial change to your CV (such as a prize, or a grant/paper acceptance if you don't have many so far) could be worth an update, but you should not ask a staff member to run about making minor tweaks to your file.