Webmaster for site edits and updates

Project Description:
I am in need of a highly capable person who can edit existing websites (HTML, wordpress, Joomla, magento, opencart, etc) to add/remove new features and content as needed. Some things I may need done would consist of: editing the PHP files of various sites, adding content via the backend, creating new pages, adding/removing products, adding plugins, moving a site from one domain to another, editing Wordpress, Magento and Joomla! themes. Basically I need someone who can handle almost any web-related task. Some things may be just utilizing the backend to add content and images, while other times I may need someone to troubleshoot an error message or edit a PHP file. You need to be available for at least 10 hours a week to start, and must be able to return work in a timely manner. This is an ongoing position as I have many websites to manage for multiple clients.