\setkeys #1#2->\def \KV@prefix {KV@#1@}\let \@tempc \relax \KV@do #2,\relax ,
#1<-blx@bib2
#2<-keyword=foo
{\def}
{changing \KV@prefix=macro:->KV@blx@bib1@}
{into \KV@prefix=macro:->KV@blx@bib2@}
{\let}
{changing \@tempc=\long macro:#1->}
{into \@tempc=\relax}