This article is a bit outdated now. For the most up to date way I create themes, see the themes for this site, which can be viewed in the github repo: https://github.com/jeffymahoney/loopduplicate.com/
With the Field Conditional State module you can change the state of any supported fields form element depending on the content of other fields. This is done by providing an UI for Drupal's States API.
All the changes made to a form by FCS (Field Conditional States) utilize only the States API and therefore are clientside only.
Normally, when a Views field has been assigned both an exposed filter and a contextual filter, then both filters get applied to the View's results set -- always. This is not configurable behaviour. It's hard-coded.