this man speaks truth. if u can't leave it alone, then the only option is to put one coat of a solid oil stain on top, but you will no longer see much of the wood. it'll be like a paint, but when it fails, it will fade rather than peel likeYou will have to strip it off or wait until it fades. Its not recomeded to apply a second coat of stain unless its wet on wet and also if you applied another semi transparent you will still see the color from the semi transparent that's applied now. If you apply another coat of stain to soon you will be over applying. If it was me I would not stain over it.
Who is they? Didn't you have a contract? Sign off on color and stain choice selection?