it can be applied to every change one might possibly make in one's behavior.

And it would be correct to deny that a change that would possibly be made to one's behavior is "such a cheap change" that we don't need to weigh the cost of the change very much.

Your discounting of non-human life has to be rather extreme for "I will have to remind myself to change my behavior" to out weigh an immediate, direct and calculable reduction in world suffering.

That only applies to someone who already agrees with you about animal suffering to a sufficient degree that he should just become a vegetarian immediately anyway. Otherwise it's not all that calculable.