...
use Foo::Core::Specialized qw(Mixed func_a, func_b, :TAG_A);
...

##</code><code>##

### From Foo::Core::Specialized
use Foo::Core;
sub import {
    my $this_pkg = shift;
    my @imports = @_;

    ### Catch the word "Mixed" in the import list and react to it,
    ### removing it before continuting.
    foreach (my $i = 0; $i < scalar(@imports); $i++) {
        if ($imports[$i] eq 'Mixed') {
            do_something();
            splice(@imports, $i--, 1);
        }
    }

    ### The goal here is to switch to the calling package, do the
    ### import from the Foo::Core package into that calling package,
    ### then switch back to this package.  The problem is, it 
    ### doesn't work... there's no error, but the symbols aren't
    ### exported (anywhere I can find them =) either.
    my $caller = caller();
    eval "package $caller;";
    Foo::Core->import(@imports);
    eval "package $this_pkg;";
}

##</code><code>##

...
use Foo::Core qw(func_a, func_b, :DEFAULT);
use Foo::Core::Specialized 'Mixed';
...