Is there a way to get a permanent access token using OAuth 2.0 method?

What do you mean by permanent access token? The token issued with suitecloud tools are valid for an unlimited time unless revoked from account. You can execute

Suitecloud account:setup

in node cli Or

Sdfcli authenticate -authid userDefinedString

in javaCli

Access Token has 3600secs of lifetime. NetSuite user can’t change this behaviour.