int addpoint(int geohandle, int point_number)
Creates a new point with all the attributes and group memberships of the point with the given point number.
int addpoint(int geohandle, vector pos)
Creates a new point with the given position.
A handle to the geometry to write to. Currently the only valid value is
0 or geoself, which means the current geometry in a node. (This argument may be used in the future to allow writing to other geometries.)
A point number for the created point, or
-1 if the point could not be created.
You can use the return value with setpointattrib to set attributes on the new point, however it may not be the final number of the point.