Replace BB?

I have a problem, my character is transformable. I made a BB for the airplane mode, it looks like a coffin and everything is fine. However, when I transform my character into a robot - the BB does not fit anymore. I tried to replace the mesh of the BB, but seems like for collisions nothing changed. What would you siggest me to do?

You ran into one of the biggest limitations remaining in the BGE, there’s currently no support for dynamically updating the bounding box for collision whether using the bounding box or the mesh itself for collision data. The only way is to replace the object with a new one or use multiple objects jointed together and moving independently. I think it may be possible to add or subtract from compound objects as well to make it seem like the collision mesh is changed.

This really should be added, it will greatly ease the making of games like this.