Custom Instrumentation

I'm currently working on a series of Christmas music arrangements. My friends asked me to write them so we can wander around the neighborhood and play during Christmas time. It's an unusual instrumentation format. 2 Clarinets, 1 Trumpet, 1 Trombone, 1 Tuba, and 1 Bell Set. I also often write for an all cello quintet. A feature where you can make your own custom instrumentation and then save it to use later would be something I would use very often and maybe others too.