All Taken:
Why do you think Apple remove the LCD itself from the iMac to clean it? They don't - they clean the iMac glass panel and clean the LCD inside the iMac. No removal of the display is required.
Okay, please note, this is the situation 1: No removal of the display is needed, neither by Apple nor by anybody else. You speak about cleaning the display (LCD) "inside the iMac", but, if you just lift the glossy glass, you are not "inside the iMac" and of course, you are not inside the display. You reached just the outer surface of the LCD, the outer side of the display. This kind of cleaning was a thousand times a theme in indefinite threads and youtube videos in many ways.
Your explanation is completely right, there is a foam sealing around and that may become untaught.
Please be patient and note the situation 2:
You are going on after removing the glossy glass (I put it always into the cover sheet the iMac came with.) and unmount the display-unit, in order to open it and to clean it at its inner sides.
This thread is the story and the pictured guide of the theme-starter Oggy, who was the first, who opened the housing of a display unit, who disassembled a display after unmounting it from the iMacs frame.
I have seen your SSD-thread, so you are expirienced in unmouniting displays.
You have to loosen the eight screws, unplug the three or four cables on the back side....
and after that you open a few points at the frame of the display housing to unfold it like a book to get between the "pages".
Please read this thread from the beginning, it is the big achievement of Oggy to show the Users World how to clean a display on its inner surfaces.
I made this with the display of an 24" iMac early 2009.
And some thirty or forty other guys did also.
If you have any questions, please ask.