Can an EU member state recall or change their nominated commissioner in the European Commission, mid-way through a term?
No, a commissioner is nominated by a member state but s/he is not a representative of that state. They are not supposed to get instructions, be recalled or be otherwise influenced by their state of origin. The same is true for judges in the EU court of justice, who are named by a member state for a fixed term mandate but approved (and potentially revoked) by the court itself.
The most senior representatives of EU member states at the EU level are the permanent representatives, who prepare Council meetings.