The @setflag() function takes two arguments: a number, and a string.
It will set the flag specified by the string on the object specified 
by the number (or unsets it, if the string starts with !). For example, 
to set the dark flag on object #123, do:

@setflag("123", "dark")

To remove the jumpok flag from #321, run:

@setflag("321", "!jumpok")