REA does not implement 6 months in country A and 6 months in country B as part-time work. In the MSCA IF, part time for personal or professional reasons allows researchers to reduce their full-time daily activities. The researcher currently working for the MSCA project in country A should suspend the action to go to country B for a period of 6 months.
In any case, the beneficiary should contact the REA Project Officer in charge to discuss more in details the part-time project implementation.