Simon Hudson, PowerShaper project member- raised the query. Andy Hamilton has given an initial (informed) opinion that:
Converting a Mitsubishi ASHP for cooling could be difficult.
It is possible to install a small, reversible, air to air system as an extra - or use super-white paint on the outside of the house. (to support cooling)
I hope this helps as a starter for ten.
If people have ideas for Simon, please do add to this thread.