amayam, you cannot, in this case 'attack the issue from both sides'. If your model is not tip stalling, then anything on the wing tip won't help, other than adding drag and weight. So far as the weight control is concerned, then it is probably too late, this needs to be addressed at the design stage. However, if you wish to do something about it, and have the time to start stripping the covering and rebuilding, then start at the tail. Anything lost here will perhaps triple the weight loss as you remove weight from the front as well, to maintain balance. Rebuild the tailplane and fin in light strip and laminated outlines and ribs, then brace to the hinge spars with 40lb fishing trace or similar. Start rebalancing by first removing any ballast, then start moving batteries around first. If you want to '3D' (I always thought all my models were '3D') and snaps are part of your flight, then anything on the wing tips that reduces the ability of the wing tip to stall will also reduce the ability of the model to snap, as snaps are stalled manouvers. So remove them, if you have them. On models like this having a big heavy steerable tailwheel is nonsense, a simple wire skid will work just as well and save maybe half a pound at the front. You could also remove any foam turtledecks, if you have them, and replace them with a few stringers and recover, foam has no structural strength. Other than that there isn't much you can do, other than redesigning and starting again. I note that you have servos at the tail, removing them to the cabin area and using cables will certainly help.
Evan, WB #12.