Maxscript: Demonstrates how to flip/mirror a transform around another transform.

Flip or Mirror Transform | .ms

delete objects
tp = Teapot radius:5 pos:[40,0,0]
pt = Point pos:[20,0,0] size:5 wirecolor:red

fn mirrorMatrixFn
    axis:"x"  --Axis to mirror over
    flip:"x"  --Axis to flip
    tm:(matrix3 1)  --Matrix to mirror
    pivotTm:(matrix3 1) --Matrix to mirror around
   =
(
   fn FetchReflection a = 
   (
 	  case a of (
 	  "x": [-1,1,1]  -- reflect in YZ plane
 	  "y": [1,-1,1]  --	    in ZX plane
 	  "z": [1,1,-1]  --	    in XY plane
 	  )
   )
 
   aReflection = scalematrix (FetchReflection axis)  
   fReflection = scalematrix (FetchReflection flip)
 
   --calculate the mirroredTM 
   fReflection * (tm * (inverse pivotTm)) * aReflection * pivotTm 
)

flippedTM = mirrorMatrixFn pivotTm:pt.transform tm:tp.transform
dup = copy tp
dup.transform = flippedTM

Thanks, works great.