When you turn on "Include Actual Execution Plan" and run a query in SSMS, the resultant plan can include information about missing index(es) that would make the query more performant. In that case, right-clicking the plan and selecting "Missing Index Details..." will script out that missing recommended index to a new window.
I'd like to modify the template for generating the missing index to conform to my organisation's SQL style guide, but I can't see any where or how to edit how that index is generated. I'm aware of SSMS templates which can be tweaked, but can't find any reference to this particular template anywhere. Does anyone know if it's available for customisation, and if so where?