Leaf Guard only prevents status conditions when its sunny weather before you get a status condition, so it won't cure it. Leaf Guard only activates if weather is set up first then you have a status conditions. It would be the same for Skill Swapping Leaf Guard as well. If you have a status condition, then harsh sunlight becomes the weather condition, Leaf Guard will not activate. For example, if you are poisioned, then set up weather, the poison won't heal.