Surely, VBB, the damage was done when the lintel was inserted and careful removal now would result in little (if any) further damage. I am not an archaeologist so please correct me if I am wrong here. In conservation the procedure is always (unless there is a very real danger to the original, or perhaps for aesthetic reasons) to remove later additions to an object while ensuring the original is made safe.

There is also the argument that leaving the lintel in place offends, "... the spiritual beliefs of some people."