This is a wish for Rhino7+ as I doubt you can implement it in RH 6, even 7 is doubtful if you don’t see the benefit it can bring.
- POINT (ORIGIN)
- LINE (AXIS) / UNIT VECTORS (1,0,0) , (0,1,0) , (0,0,1)
- Rectangle/square or squared planar surface.
These must be immutable objects but selectable to be used as reference
COPY, MOVE, OFFSET, EXTRUDE, ROTATE, etc. should create instances of mutable objects.
In fact simply replace the current abstract gimmicky object that defines the UCS with a compound of these point three lines (for the axes) with option to show also the planes.
NOTE: As an alternative for Rhino6 perhaps you could add a way to lock objects but still be able to select them as reference/copy/extrude.