Newbie wants help with altering base frequency

[viola78960]

I want to work with an alternative tuning. Can someone tell me how to correctly reset the base frequency for a scale? I thought I would copy a file and rename it as a new file, and make the alteration,

OR can I reset it globally, for the entire program?

Also if someone could tell me which file is the equal temperament file (the one commonly used for the piano, etc.), I would appreciate it.

And it would also be helpful if anyone knows which just intonation scale (filename) is suitable for the viola.

Any help would be appreciated.