Open and close AGAIN [closed]

Not a trivial question. Again is an adverb. Again = back to the original place or condition or “once more or as before”

Cambridge dictionary

“Get some rest and you'll soon be well again.”

In your example “Close the window again”, it is difficult to regard again as an adverb qualifying close. Rather, it seems to refer adjectivally to the previous state of the window rather than to the verb.

Another viewpoint is that the sequence of events is: Window closed - window opened - window closed again; or Sitting - stood - sitting again. So perhaps “again” refers adverbially to the unexpressed past participle adjectives such as closed in window closed.