Hi! Thanks for reaching out.
It is possible to get a strictly black and white export presently, but it would involve writing code to modify the color replacement logic in the manifest.tds script file of whichever sprite style you are using.
The simplest solution would be to modify the exported texture to comply with your intended palette (black and white in this case) in a pixel art editor or raster image editor like Aseprite, Photoshop or Stipple Effect as a post-processing step.
It’s unlikely that I’ll specifically add 1-bit B&W export support in an upcoming update.