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While it is a bit of a gray area, there's nothing that strictly prohibits a change of plans after the receipt of a visa. There are stories of people getting in trouble when they use their visa for a purpose other than that shown in their visa application, but the basis for this trouble is suspected fraud rather than any explicit rule against changing plans.
That is, you're not allowed to lie about a plan to visit Greece when you really want to visit France. People might do that if they believe that the Greek consulate is less likely to refuse their visa application, or if the Greek consulate is more convenient to travel to, or if the Greek consulate has appointments available when the French consulate does not.
Based on the facts presented in your question, however, your hope to travel to France on a Greek-issued visa has nothing to do with fraud or other deception, so you should, in theory, be fine.
As I've mentioned, however, it is a bit of a gray area, not only with immigration authorities, but even more so with airlines. You may want to check with your airline about this before you travel, to minimize any negative impact.
When you enter the Schengen area, you may want to avoid bringing up your change of plans voluntarily. You might mention it if it comes up naturally in the conversation with the passport inspector, and you should certainly mention it if asked directly.
You should also bring any legitimate documentary evidence you have that shows what happened. To be thorough, you will want to should
You might also consider asking Greek or French authorities about this; keep a record of any such communication so you can show it to the airline or to anyone else.