void Ni_SetModified( Ni_node restrict n, int modified, int recurse );
Sets the "modified" state for a node or tree/subtree.
n (in) should be the Ni_node whose "modified" state to, well, modify. If recurse is nonzero, n should be the root of the tree or subtree whose "modified" states to set. If n is NULL, the function has no effect.
modified (in) should be what you want the "modified" state to be for the affected node(s). It should be treated as a boolean value, so use nonzero for "modified" or 0 for "not modified".
recurse (in) is a boolean value for whether to recurse into the (sub) tree with n as its root or just process n itself. Obviously, 0 means don't recurse, just set n's "modified" state; nonzero means the other.
See Ni_GetModified() for an explanation of the "modified" state and how it's useful.
The "modified" state is automatically set (non-recursively, obviously) by each of the Ni_SetValue() functions.