Musescore 4 - Duplicate instrument
It takes quite a while to add new instrument, set its names, brackets, staves, and VST with all the settings configured.
Please add the ability in the Instruments side panel to secondary-click an instrument and choose "Duplicate". Clicking this will duplicate the instrument, with all its settings, notes, VST configuration, and place it below the selected instrument.
This will greatly decrease the time it takes to setup a custom template