I have evaluated your scenario/ case a bit in MS Excel manually. Well, when you protect a worksheet, it will also lock the objects including Chart or other binary objects and there is no Locked option available for chart shape either. You may either lock objects including charts, pictures and other binary objects or set them unlocked for editing while protecting sheets, you may confirm this behavior in Ms Excel manually. If you still think that you can achieve your desired behavior in Ms Excel manually, kindly create an Excel file with your desired task, save the file and provide us here, we will check it soon.