Would it be acceptable to select an appropriate ability for the spellcasting ability depending on the circumstances?

Would it be acceptable to select an appropriate ability for the spellcasting ability depending on the circumstances or the nature of the spell like for instance using Constitution for the Contagion spell? Acceptable to the rules as written? No.

The DM can, of course, do whatever.

— Jeremy Crawford (@JeremyECrawford) June 11, 2018