I've never heard that anything changes in regard to the Antimitsion when a bishop resigns or resposes. In my parish, when Bishop Maximos of Pittsburgh became the diocesan hierarch in 1979, after the charter change, he did not issue new antimitsia to replace those issued previously by Archbishop Iakovos, but antimitsia with his signature were issued to new priests in our diocese. Metropolitan Maximos retired last month, Metropolitan Nicholas of Detroit is our Locum Tenens and he did not issue new antimitsia. I did notice, in the GOAA's Archdiocesan District, some time after Archbishop Spyridon had been enthroned and during his tenure, he issued new antimitsia to the priests of the (Direct) Archdiocesan District, the priests who are directly under him, but it was quite a bit of time after his enthronement, two years perhaps. When Archbishop Demetrios was enthroned, he promptly provided new antimitsia to the clergy of the Archdiocesan District soon after his enthronement, at a ceremony at the Archdiocesan Cathedral. My metropolis is currently widowed, so we'll see after the enthronement of the new metropolitan, if he issues new antimitsia.
Aren't antimitsia prepared during a church consecretion? If so, how could a new diocesan bishop issue new antimitsia until he has consecrated a church?