If you mean as a score templet in MU4, it already is. When you set up a score look at the right of the window where it says "Order: Orchestral" . Select the down arrow.
Also, all the brass band instruments should be there, just use the search box or set the dropdown to "all instruments" instead of just "common". The default soundfont might not have separate sounds for all instruments so it will substitute whatever is closed, but you're welcome to use any other soundfonts or VST instruments that provide additional sounds.
Comments
If you mean as a score templet in MU4, it already is. When you set up a score look at the right of the window where it says "Order: Orchestral" . Select the down arrow.
Also, all the brass band instruments should be there, just use the search box or set the dropdown to "all instruments" instead of just "common". The default soundfont might not have separate sounds for all instruments so it will substitute whatever is closed, but you're welcome to use any other soundfonts or VST instruments that provide additional sounds.