Aah! So, you question
is about the person consecrating the Eucharist!
A Catholic priest who leaves ministry loses his faculties (other than in exceptional cases, (i.e., Reconciliation for a person in danger of death)). So, a Catholic priest who has left the Church in order to serve in an Anglican community would
not be able to validly consecrate the Eucharist in a public liturgical celebration. I can’t speak authoritatively, but I would expect that an Orthodox priest in a similar situation would not be able to consecrate the Eucharist in a context outside of the Divine Liturgy.
It’s my understanding that the Church considers the Eucharist consecrated in a PNCC liturgy to be valid; however, that speaks both to the priest and the liturgy, and not to the person of the priest by himself.