Rewriting taxonomy term in exposed filter
The easiest way is to use hook_form_alter to alter the names displayed in the options.

An alternative and a bit more tricky way, is to create your own views_filter_handler for them term used in the view, and customize how the exposed filter form should look like. This is a good solution if you are creating many views and want a single place to do the alterations. See How do I add dropdowns in Filter Criteria in Views module? for more info.