Hi!
You can use a custom css in the page code or in archive output template with !important to override your theme’s css.
On the other side,you can use a plugin which allows customizing backgrounds on pages: http://wordpress.org/plugins/background-per-page/
You can remove dashed underlining by correcting strings #1306 and #1317 in your theme’s css.
For text corrections, need to see the theme.
