Is it possible to change the Eclipse branding without modifying/building from source? Like:
On an Eclipse application downloaded from the eclipse website.
That kind of branding is usually specified by a branding plugin, which is often the same plugin that contains the product definition (in the plugin.xml). Ex: *eclipse/plugins/org.eclipse.platform_3.8.0.v201110251800* contains the org.eclipse.platform.ide product.
Branding plugins are often deployed in the directory format (as opposed to jars), which would allow you to modify some of the files in your installation ... as long as the plugin is not signed.
The correct way to do it would be to create your own product and your own branding plugin and then build the product again ... but you would have to figure out what it takes to launch the application you are using.