Registry keys for Excel file associations

I have this problem where Excel 2016 keeps taking over my file associations from 2010.
I want to create a .reg file so I can force the Excel file associations back to Excel 2010.
To do this, I need to know which section of the registry to alter.

Anyone?

(Not interested in the following 'alternative' solutions:

1. opening files by opening the program then selecting File Open
2. setting the default program by "right click, Open With". Does not work for me (2010 does not appear. If I folder drill down to the Exe, it doesn't appear on the program list so I can never set it as the default program)

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