Cecilia:
Probably the first thing to know is whether this is an object you are staring from scratch, or a modification of an existing marker.
To add the center line, find the place in the 2D Script where the circle is drawn (probably with an
Circle2 command, but could be
Poly2 command). The radius of the circle will be described here, so you can use this data with the
Line2 command to draw the centerline.
The text is tricker, I generally advise users to start with a standard marker, which already has the code for the ID text, the custom text will be simpler, but getting the placement and rotation/mirroring can be complicated.
HTH
David