There are three big changes, which I'll take in turn.
A reasonable guess is that its new target is to push inflation up to 2.5% over the next few years.
"Our inflation target is now x%" would be much clearer than a back-door redefinition of what "average inflation" means.
An inflation target works well when it's widely understood. This ain't it.
But opaquely raising it by 0.5% seems like fiddling at the margins. Is a half point really aggressive enough? (It's not.)
I buy the argument for flexible inflation targeting, but the Fed's strategy changes are timid, as if it hasn't convinced itself.