You don't need to reboot.
If I edit a config file? Normally changes don't take effect until you reboot. Or "restart X" which still requires closing and reopening all the stuff you were working on, so it may as well be a reboot. The GUI tools on the other hand apply the settings right away.
Played around in those files but really not sure what to edit. There's various xml and non xml files all over and it seems to vary from theme to theme. Would be nice if they had a GUI tool like in Windows. The gnome tool is closest thing but the scrollbar option does not do anything.
Edit: I sorta got it to work, it's really finicky though. The options don't do what they mean. "Button pressed" for example is the colour of the entire bar while normal is the scroll bar button part itself. You also can't do it to the default theme, you need to set a specific scrollbar theme. The options change around depending on what theme you pick. Really odd. Works now anyway, without having to edit files, just really missleading options/settings and have to really mess around and pick different themes till one works.