Hot to create a custom size one way mirror

Hello Everyone,

What I need to do is to edit the existing one way mirror in to a customizable size one. So I need to create the middle without the end of the window with one space foot print and then separate the end of the window to be added when I need to window to end.

Let me attach an example to be sure I make me clear.

Example and Here



Anyone could guide me how to do that ?


Thanks, Laura

PS: I'm new here hope I post in the right category.