Oh, excellent! Though be careful if you only have the 3.0 ROMs - some software may fall over with mixed versions of the OS. Yes, you can replace the icons and modify pretty much anything about the way it looks by installing patches, but be warned - they'll take up more memory when they're running, and with only the standard 2MB it'll disappear fast

Have a look on aminet.net for NewIcons and Birdie. NewIcons extends the icon system to allow for better icons (of which there are vast amounts), and Birdie lets you change the appearance of window borders, gadgets and so on. MagicWB is an alternative system of nicer icons.
If the drive came preinstalled, it may even have some of these installed! A drive I bought years ago came with MagicWB already installed.