A federal appeals court in Boston has agreed to rehear the state’s appeal of a lower court ruling that a prisoner convicted of murder must receive a taxpayer-funded sex change. In a ruling Wednesday, the US Court of Appeals for the First Circuit said its entire panel will rehear the state’s appeal at a hearing scheduled for May 8. Last month, a three-judge panel of the same court upheld a US District Court ruling that Michelle Kosilek, now 64, is entitled to the surgery. Kosilek, born Robert, was convicted of murdering his wife, Cheryl, in Mansfield in 1990. He has been living as a woman in prison.