Yeah, the #erase directive is all you really ever need.
#erase 0x800000 0x64
That directive would erase 100 bytes from the offset 0x800000.
But like HackMew said...
# #eraserange 0x800000 0x800100
That would remove all bytes from 0x800100
Removes the last compiled script from the ROM, so long as it was a Dynamic Script. (Having the #dynamic directive at the header.)
This directive would remove the main section of a script located at 0x800000 (Like how scripts have sections, this would delete the only one this points to...)
Please read the guide that comes with XSE, by loading XSE and pressing F2, OR, by navigating to your XSE folder, and double clicking 'Guide.chm'. If you are not able to see file extensions, (Like .chm, or .exe, or .txt, then just click the icon named 'Guide'.)
(LOL, not trying to stand you up HackMew, but I like giving gratuitous amounts of detail as often as possible...)