Poking around in implementation specific directories is not recommended. The preferred way of doing what you want is to use the SpringSource tool suite to deploy the application and then edit the files you want to change and save them. The tool suite will call the deployer interface to update or delete a static resource which will then be picked up by Tomcat.
That's the story with the old deployer and old web container code, but it has regressed with the introduction of the RFC 66 based web container. See: https://issuetracker.springsource.com/browse/DMS-1121.
Meanwhile, you *might* be able to get away with editing the file in the Equinox bundle file if you want to try quick temporary changes, but the caveat above still stands, especially if it doesn't work. ;-)