I'm not sure how this committee is structured and the rules around appointments, but members of many committees and boards that are part of the executive cannot be removed without cause.
Didn't he testify to Congress during confirmation that he wouldn't do this sort of drastic change? Pretty sure perjury to Congress IS extremely illegal.
IANAL but executive retainers do tend to have some protections precisely for thus reason. You don't want a shift in presidency and then for them to hollow out 4+ years of tenure to advance their agenda. There needs to be some non-partisanship so the sceicne isn't bogged down by beuracracy.
At the bare minumum, most government workers get due notice of their termination. The federal government is for the most part not at-will.
He ousted the whole group which does have more standing than singling someone out. And reasoning can be as simple as conflict of interest... Eg being unwilling to challenge pharma lobbyist current state directives
The committee is under the control of HHS Secretary... JFK. He literally has the authority to do what he did.
Changing a plan you inherited but now own is not illegal.