OK, I read many of the responses and here is my answer. Are you having the problem or is the child having the problem?
I am not trying to be disrespectful but I am unclear if his changing hands for different tasks is causing him some problems with processing or are you concerned it will eventually cause him some problems, so are trying to be pro-active before problems arise.
I have 3 boys and 2 are righties and 1 is a lefty. The lefty does switch hands for alot of things, like baseball batting etc. but eats and writes with his left, other stuff for his right. I have asked him about it and he says some things just don't feel correct in the left and feel correct in the right. But he doesn't have any problems assimilating, studying, writing or reading, or following instructions (well, beyond a pre-teen boy anyways!) ;) Plus, my oldest righty is the dyslexic. Not the changing lefty.
So, I would think that if your son were having problems then have him evaluated by the school and/or consult an OT to help him. If he is fine and handles the changes ok, I wouldn't worry.
I will tell you that my husband used to be a lefty. But when he went into elementary school in the early 70's, they forced him to be right handed. And he said it messed with him for a long time. He still has problems multi-tasking etc. and also had ADD as a child and I wonder if the school making him change his "wiring" had anything to do with his behavioral problems. I still have to write lists for him and instructions or he just doesn't process info very well.
I really wouldn't worry about it unless you can definately detect a problem. His body will sort itself out all on it's own. You also need to consider that he can be left handed but right eye dominant or right foot dominant also. So, just let him figure it out. And he will. There's no problem until there's a problem.
Good luck,
L.