TLR will a fresnel in the viewfinder change focus?

[gtyler5]

I am working on a Yashica Mat EM, its a great TLR however I am unimpressed with the dim view finder. I have a fresnel out of a Mamiya C33 parts camera that fits quite nicely. If I put it under the frosted glass will this change the focus?

 

[TimmyMac]

If the fresnel is on the lens side of the ground glass, yes. If on the viewing side, no.