Maxscript: Mirrors and object's matrix across an axis in 3ds Max.

Mirror Matrix Across Axis | .ms

--Create a point
p=point pos:[-20,0,0] size:20 axistripod:true box:true

--Rotate it 90 in z
rotate p (eulerAngles 0 0 45)

--Get the transform matrix to work with.
tm=p.transform

--Mirror the tm across the world matrix in x
mirroredTm=tm*(scaleMatrix [-1,1,1])

--Set the transform just so you can see what it has done. 
at time 10
animate on
p.transform=mirroredTm

--Mirror the mirrorTm in local space but this time on the y axis. This would be known as flipping the y. 
finalTm=(scaleMatrix [1,-1,1])*mirroredTm

--Set the transform back to the object. 
at time 20
animate on
p.transform=finalTm

Mirrors Camera across World XY Axis

delete cameras
-- frontCam = Inverse(viewport.getTM())
frontTM = (matrix3 [0.936672,0.350207,0] [-0.13119,0.350883,0.927184] [0.324707,-0.868468,0.374607] [909.75,-2617.23,1404.43])
Freecamera transform:frontTM

fn flip_matrix tm =
(
	--Mirror the tm across the world matrix in xy
	mirroredTm = tm*(scaleMatrix [-1,-1,1])
	
	--Mirror the mirrorTm in local space but this time on the y axis. This would be known as flipping the y. 
	finalTm = (scaleMatrix [1,1,1])*mirroredTm
	
	--Return the transform 
	finalTm
)
Freecamera transform:(flip_matrix frontTM)