Stu,
Don't know about the Turkish DGCA (although I once had a B-727 and B-737 endorsement on my FAA certificate from them) but as far as the FAA is concerned if you are exercising the privleges of your FAA ATP under the endorsement of a foreign entity they (the FAA) could care less what you do as long as the a/c has a registration starting with anything except "N".