I love the original creation but am not skilled enough to modify the OpenSCAD file to generate external flap pins instead of needing the metal axles.

The uploaded files shows the post processed modifications using Fusion360, in particular the vent flaps.

I joined each of the two flaps halves with superglue (cyanoacrilate) and use baking powder on the inside of the flap to set the glue and provide reinforcement.

Also, The original OpenSCAD file has a mistake at line 128 which throws an error.
I believe it may be an issue with the UK vs. US spelling. "centre" vs. "center". Once corrected all is okay.