I think ill be fine extending the battery pack. It will not effect the cg because there is a space left for the RX battery which im not using(using speed controller with cutoff). so making the pack into 8 cell pack and extending it towards the back instead of making them humpback is ok and i will not effect the cg. the space was meant to take the weight of the RX battery so it should take the 2 extra cells.

now how important is it to make the front gear steerable for the plane to take off from grass? could the rudder control be enough?