Old thread alert… perhaps start a new one?
You can change a part of an object into a modifier (r-click and change the “type”). Changing a base/single object to a modifier type doesn’t make any sense (what would it modify?).
Some threads related to designing/using modifiers drawn in CAD:
[ Set hole wall thickness ]
[ Reinforcing parts by designing modifiers in Fusion ]
[ Convertir une partie de pièce en modificateur ] (Convert a part to a modifier)
-Max