I suppose so, don't think there is a limit as long as it's under warranty.
but if it's checked by them to be within the acceptable range for focusing error, I don't think they'll do any calibration but just return the lens back to you
They will advise you against it if it is within their stated acceptable limit.
Simply because they say once a lens or body that is taken apart, when putting it back together, it might not be the same again. So they ask you to seriously consider.
i'll have to agree with this one. if you need to have calibration done so often, it might be worth asking for a replacement instead (if warranty covers the "defect").