I'm not quite sure I follow you, but:

----if the DOF-preview of an old F-1 is engaged before you attach a FD lens to the body
----if you then attach the lens
----if you then disengage the DOF-preview and remove the lens from the body
----you will hear a metallic "twang" as the aperture lever returns to it's rest position. This won't damage the camera or damage the lens.

I'm not quite sure why all this discussion about something that rarely happens. In the 40+ years I've been using FD gear, I've never had any problem with using the DOF-preview and attaching or removing a lens. This is a total non-issue, at least for me.

Jim B.