MicroPress 4x5 question

On the MPP MicroPress 4x5 camera there is a FRONT <-> BACK switch. It seems

to be locked in the FRONT position but the FP shutter works fine
in this position and I am not able to move the switch to the BACK
position. 
Anybody knows the secret behind this switch?

The camera came with a Xenar 135/4.7 lens. Is this an OK performer?

I think I have the International Back version. What does this mean? 
.....that many suppliers of rollfilm backs can be used on the camera? 
.....e.g. a Horseman 6x9 back?

Max