You can enter in and out after doing enough tasks from Alex (should be when he asks if you'd like to be his personal assistant and help or after the first trust exercise? I'm not sure, but it's after the Portal Panties and when you first meet Socket) but it'll be marked as off limits, and any Engineer pawns there will try to attack you.
Also, the area functions differently than the engineering zone in the Tavi storyline. If you enter using the first option, it won't progress, but the second one will make you do the series of actions to get the door code, and, iirc, the engineer pawns won't be there, or are replaced with something else.