jonyyybe:
You could try opening the library part and changing its Subtype to Opening > Wall > Door, but this may need additional editing of the scripts to work properly. Two other options:
1. Select a door that that supports Custom Panels and try saving your part as a Custom Panel to use with this door.
2. Place an Empty Opening, then place this object on a 3D only layer for 3D, draw the plan symbol with 2D tools.
David