I wonder if the priest can switch the abstinence to no eggs but chicken meat because eggs had become a luxury and fish is always more expensive 
I don’t think so because chicken is flesh meat. In the distant past, eggs and dairy products were to be fasted from on days of total abstinence. One needn’t eat fish on days of abstinence, either. I knew a woman who used to insist it was required for Catholics to eat fish! (I couldn’t convince her otherwise!) If you live in Florida, I suppose it’s possible to eat the excess of iguanas breeding out of control, or certain times of the year, depending upon your locality, turtles, frogs’ legs, rattle snake, snails, eels, some of which may be available free of charge. If you live in Hawaii however, DO NOT eat wild snails as many carry brain eating amoebas, 100% fatal to humans.