You may be able to repair it. The key to repairing the cracks is to repmove
all the loose material. When plaster cracks it is definitely separated from the lath. If you try to skim over the loose material the crack will come back.
You might want to take a look
here . Look on the left column for "breaktime forum". There are a bunch of builders / remodelers that hang out there. You'll probably get more info than you want!
OOPS! Welcome to TechIMO!