In a word, no. You can change a lot of the existing hud images and replace them with new ones by just making new images with the same name as the old ones, and placing them in the right directory. (data/interface IIRC)
To figure out the names of everything, you have to use a vp tool such as VPView to check out the original files in sparky_fs2 and sparky_hi_fs2. The files in sparky_hi_fs2 are for 1024x768 and higher resolutions. The interface itself has two layouts as well, one for 640x480, the other for 1024x768 and larger. To do a complete replacement, you'll need to replace both the low-res and hi-res sets of files. Or you could just change one set, and tell people not to use the resolutions for the other set.
Some things on the HUD can be moved around and changed with hud_gauges.tbl. Not very many things, though.
And if you want to do something completely different, you have to override everything and learn scripting. This will work for very minimalistic HUDs, but it's difficult to do things like radar in scripting, and other things (like the auto-target and auto-match indicators) aren't really supported at all.
It's easier than it sounds.
