Set or generate a new HD wallet seed. Non-HD wallets will not be upgraded. Only for legacy wallets.
newkeypoolbooleanoptionalseedstringoptionalcurl --user myuser --data-binary '{"jsonrpc":"1.0","id":"1","method":"sethdseed","params":[]}' -H 'content-type:text/plain;' http://127.0.0.1:8332/null