How do I disable and enable macros on the fly?

As far as I know, you can't enable / disable macros from an opened workbook on the fly.
Yet, you shouldn't have to because macros are only triggered thanks to a user click.

The only case I would see is for the Event Procedures (Worksheet_Change or else).
You could then create procedures to activate / deactivate events and call them from buttons in your worksbook:

Sub enableEvents()
    Application.EnableEvents = True
End Sub

Sub disableEvents()
    Application.EnableEvents = False
End Sub

You can also try these tips from Chris Pearson website using global vars you would change depending on your needs:

Public AbortChangeEvent As Boolean

And check if afterwards:

Private Sub Worksheet_Change(ByVal Target As Range)
    If AbortChangeEvent = True Then
        Exit Sub
    End If
    '
    ' rest of code here
    '
End Sub

To disable macros on the fly, use "Application.EnableEvents = False" via the Immediate window in the VBA editor (and "Application.EnableEvents = True" to turn them back on).

You can also hold down SHIFT when you open a document to disable macros.