The CORE One's firmware requires that the door is closed to do axis movement or filament loading/unloading. This is for safety/legal reasons and won't be changed. In order to leave the door sensor enabled and only trick the door sometimes, this small print magnetically attaches when needed.

In theory, any filament with any layer height (Hatchbox Orange PETG with 0.2mm STRUCTURAL shown) should work. A bright color is recommended so that it stands out, as the print prevents the door from closing. 2 6x2mm magnets are required (unless modified, like 5x2mm magnets) and should friction-fit with no glue required.

Note: this goes against something in EN ISO 12100 ("Safety of machinery — General principles for design — Risk assessment and risk reduction"). Only use this when doing maintenance, not for active printing.