The (bogus) text in the provided STL is fixed in place: you want to take the .scad file and make your changes in OpenSCAD. I would recommend using a new (possibly Development) version of OpenSCAD and enabling fast-csg or Manifold in the settings before you render, else it could take a very long time to finish. I used 2023.08.25 (newer should be fine), which renders quickly with Manifold enabled. 

Requires BOSL2.