Opt out of Medicare Part A

[SLuskin]

If a 66 year old, who is not receiving SS retirement, and is enrolled in Medicare Part A, but not Part B, goes to Medicare and dis-enrolls from Part A, can they then make a contribution to an HSA account? Do you know is there is any negative in getting out of Medicare Part A, is there a penalty to get back in if they were employed and covered by group insurance.