How do you split open a menu class?? (Garland theme)

Hi - I'm modifying the Garland Theme - I'd like to be able to make the following Garland menu class output (from a primary link) <li class="menu-1-2-2-active"><a href.... etc to become <li class="menu-1-2-2 active"><a href.... i.e. to separate out the active part from the rest of the class name (for sliding doors). Is this easy? Thanks in advance, Duncan