If you are saying that one year the foliage seems large and possibly reverted and the next year it is normal on the same branch then this would be normal for the most part.

Japanese maples will often throw out large atypical foliage on frist year wood or when conditions are very good. The next year on the older wood the foiliage will be typical.

When the supposed reversion encompasses a second season, then it should be cut back. Reverted wood in maples can quickly overtake a tree so that there will be nothing left of the original cultivar. But leaves of various shapes and sizes can appear on the same tree in a given season but should become normal in the next.

For now, it their are significan areas of the tree your friend is concerned about, the branches should be marked with some green garden tie or ribbon and monitored to see if the next years foliage is normal. Once your friend gets to know the tree and its tendencies, he will know what and when to prune.

FYI, Beni kawa is not known to revert normally. Likey just atypical foliage that will become normal.

Michael

I wouldn't cut any thing off. Next years growth will more than likely be normal. It may caused by fertelizer. Most of use very little on Acer Palmatum and their relatives.