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How do the tenses in English correspond temporally to one another?
Mira is wondering what is the correct way to say: "Once the client has replaced the songs" or "Once the client had replaced the songs"? this describes an action that will take place in the future, and the question is regarding the result of this action.
For your requirements, something happening in the future, "has" is a valid form. I'm not able to tell you the grammatical name for this construct:
Once the client has replaced the songs, he must restart the player.
Although "has" usually refers to the past, here we are talking about a moment beyond that time. When the client restarts the player, the action of replacing the songs is in the past.
"Had" would mean that the whole series of events happened in the past:
Once the client had replaced the songs, she restarted the player.
(I have assumed throughout this answer that the client is a "he" or "she", not an "it")
If I understand your question correctly, since the action will take place in the future, the following should be used:
Once the client replaces the songs, ...
