I played Eve Online for a long time, and like many other MMOs there was a "test server" where you could fly every ship, had perfect skills, unlimited money and so on. This was a great place to try out fleet theories, test new builds against friends or indulge in tournaments with your corp mates.

How about a similar Test Bed in bloodbowl? You can create a team, add as many spp as you want to "spend" and build teams to try out strategies and give yourself a team build to work towards. At the end of the match, the teams are lost and the result recorded as usual but doesn't count for anything. It's just a sandpit to mess around in.

Combine this with optional rules to try out - like changes to PO or Claw etc or the penalties for fouling or even changing other more fundamental rules if you so wish. In this way, if a coach had an idea for a rule change they could present a "proof of concept" over a few matches.

Just a thought.