bariton in B

Please give more information.

A bariton what??

Are you referring to B as in German parlance or as in the rest of Western Music??

I will assume you are referring to the instrument known in English as baritone horn, and that you are referring to the German "B", which most of us know as Bb.

Most of the world treats the baritone horn as concert pitch instrumenta, reading bass clef, but there is a segment of the world (mostly marching bands in the UK and schools in the US as far as I know) that treats them as Bb instrument and puts them in treble clef. You have two choices here. You can add the baritone normally then change its clef (simply drag a treble clef to the first measure) and then change the tranposition (right click the staff, staff properties, then see the controls at bottom). Or, you can define a new instrument in instruments.xml that will automatically be added this way. I also wonder if the brass band templates aren't already set up that way?