Does this have the desired effect?

{
package Foo;
sub f { "default f\n" }
sub g { "default g\n" }
}

sub localized(&) {
    local *Foo::f = sub { "localized f\n"; };
    local *Foo::g = sub { "localized g\n"; };
    $_[0]->();
}

localized {
    print STDERR Foo->f, Foo->g;
}
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