I would watch that behavior - it could indicate a respiratory infection. In my experience, ball pythons don't hold their mouth open in that manner unless they are having difficulty breathing through their nose. Since they are unable to cough (no diaphram), they will from time to time open their mouths slightly to breath better.
Given all the handling it seems that he gets, stress and no consistent temps (in and out of the enclosure often) often contribute to respiratory infections.
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