PIP medical - advice please

Hi all, I’m need of some advice - I’ve just received my PIP medical date for 08/06/19 ....

I’m suffering from T12 and L1 superior end plate fractures, and osteopenia of the lumber spine (I have a constant pain rating of 9 out of 10), both my Spinal Consultant and GP have told me - NO lifting, NO bending, standing for SHORT periods only - the DWP were made aware of this when I completed the PIP application, and are in receipt of covering letters from the Spinal Consultant and GP. My concern is that the medical professional will ask me to perform movements that could seriously damage my recovery, and/or affect my long term health.

What I would like to know ..
.. (1) can I refuse their request to lift, bend, stand, if I feel it could be decremental to my recovery and/or long term health, and/or would cause additional pain and/or injury - would I be penalised for this refusal?
.. (2) can I write a letter detailing my concerns, stating they must accept full responsibility for any injury sustained through their requests - do they have a duty of care to sign it, or can they dismiss the letter and/or refuse to sign it?

Thanks in advance.