It is not the weight that is the reason to make charges lighter. It is the length of the bullet. Decreasing case capacity requires reducing a load. Though the load you have is for the same mold of the bullet you have cast so do not sweat it. The length of the bullet is the same so starting at the starting load is the thing to do. Though do not go hog wild loading up a bunch at starting load until you get a chance to shoot a few. The light loads may not be hot enough to cycle the action of the gun you are using. If so then increase the charge by two tenths of a grain at a time until it does.
Though I applaud you asking the question before doing something. Even if the seasoned reloaders may give you some flak it is good to know some will ask question before doing something not to bright.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.