This "Thing" attaches magnetically to a steel ceiling register vent to deflect the air that normally moves left and right, as directed by the exterior stationary vent blades. The air that moves forward and backward, as directed by the interior adjustable blades, is unaffected.

Customizer

The OpenSCAD code is configured for a Ceiling Register Vent with exterior dimensions of 29 cm long x 19 cm wide. It can be adjusted to fit any such vent, constrained only by the size of your 3D printer.

Printing

The "Make" requires no supports.

Assembly

I used strong (N52) rectangular neodymium magnets but lesser strength (N42, N35) such magnets should work too. Using double-sided tape, I affixed the magnets on the outside, as shown in the picture, so the bottom of the feet are flush with the Register Vent. If you have weaker magnets, you can affix them on the inside of the feet, against the steel Register Vent. In that case, you may need to use cyanoacrylic glue instead of double-sided tape to affix the magnets to the feet.

My "Kit"
Printer: Ender 3 Pro with Creality glass build plate
Firmware: Marlin 1.1.9.1 with manual 3x3 bilinear mesh leveling
Manager: OctoPi v0.17.0 running OctoPrint v1.6.1 (Python 3.7.3) with Pi Camera v2 (8 MP)
Slicer: Cura v5.7.2
PLA Filaments: Atomic Filament, Eryone, GizmoDorks, 3D Fuel Pro

This "Make"
Used no support or adhesive aids
Atomic Filament (Bright White )
Cura Slicer Settings: Standard Quality (0.4 mm nozzle, 0.2 mm height, 200 C nozzle, 60 C bed, 20% infill)