The only way to rename an instance is to uninstall/reinstall.

Yes.

That code throws an error.
Msg 4104, Level 16, State 1, Line 66
The multi-part identifier "ic2.object_id" could not be bound.

Can you post the working code that...

Pages in SQL Server are 8KB.

The script you posted works.

Check the name you're putting in the WHERE clause, and check if your DB is case sensitive, if it is the case will matter...

If the certification site doesn't list prereqs, then there aren't any.

fwiw, MS exams don't tend to have pre-requisites, but the certifications require certain exams, so check which exams...

Upgrade to SQL 2016, because Query Store
and some other nice features including the availability of some previously Enterprise-only features in Standard and Express with SP1.

The 'word wrap' (or removal of) is doing some odd things to code.
eg https://www.sqlservercentral.com/Forums/Topic1850494.aspx

And having spaces lost like that makes it really tricky to reformat the code,...

You're missing a bracket after the GROUP BY in your subquery

GROUP BY C.AccountNo, MONTH(T.CreatedOn), YEAR(T.CreatedOn) /*needs a close bracket here*/ B On A.CID=B.RefID

Are you creating the index directly on production during a time that the server is active? If so, the create will definitely take longer than it would otherwise.