Mandatory Reconsideration - just for the mobility section

Hi all. My husband and I are shielding. After applying for PIP in January, he had a telephone conversation with assessor and has been awarded standard for living but nothing for mobility section.   He has just been medically retired due to ill health and due to ankylosing spondylitis for years is in constant pain which makes it difficult to walk, although he can but he struggles and stops and starts. Does anyone know if we ask for a mandatory reconsideration just for this mobility section if they can take the money just awarded away if they disagree with our mandatory reconsideration? I am not sure it's worth the risk as he wouldn't go to a tibunal appeal he says. I know they can alter a decision at a tribunal but can they alter it on the mandatory reconsideration?  Thanks for your help.