Hello @brianwclayton1969,
your question was clear from the beginning.
In the picture below I explain the relationship between Views, Connected View templates and the Project Browser.
- A View can have a View template connected (1).
- A View template has View properties settings (2) based on the View Type (3).
- The properties are connected to the View Template if the "Include" option is set (4).
- Your 'HVAC' (5) Sub-Discipline is a Project parameter that is connected to 'Views'. See the Manage tab, select Project parameters, select the parameter 'Sub-Sisciplie', click Modify and check the Category that it is attached to.
- The Views in the Project Browser are arranged based on the parameter values of your Views.
So if you change the Sub-Discipline in your View Template to "Plumbing", it affects all Views that have that View template connected (1).
In your project browser, they will move to "Pumbing" (6)

So when you want your existing Views, that have the View Template "Mechanical Plan" connected, stay where they are, you don't change them.
You duplicate that one, give it a proper name, and change your Sub-Discipline to Plumbing. Change other View properties and add that View template to your New Views.
Note:
For your company standards, it is very important that you set up your View templates right and connect them to your Views.
I hope this clears it up. 
See also this screencast: View Templates
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Kind regards,
Robert Klempau
Senior Consultant AEC
Cadac Group AEC BV