How to Change the File Extension for a Data File

Link Below:

How to Change the File Extension for a Data File

In general, the file extensions that we use for SQL Server data files are MDF (Primary Data File), NDF (Secondary Data File - this is optional), and LDF (Transaction Log File). SQL Server works fine with any file extension but Microsoft recommends we use MDF, NDF and LDF. 

But, a different file extension also work with SQL Server.

This article helps in finding a way to rename the file extensions.

Changing the Path for the Master Database

Link Below:

Changing the Path for the Master Database

This article will show how we can move the master database to a new location.

The ALTER DATABASE command would work for moving all the user databases and some system databases, including model, msdb and tempdb, but changing the path of the master database required a different strategy.