bar.pl:

#!/usr/bin/env perl
use warnings;
use strict;

use Foo;
use feature 'signatures';

foo(9,10);

sub foo($x,$y) {
    print $x+$y,"\n";
}
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Foo.pm:

#!perl
package Foo;
use warnings;
use strict;

sub import {
    warnings->unimport('experimental::signatures')
        if $] >= 5.020;
}

1;
[download]

Foo.pm with Exporter:

#!perl
package Foo;
use warnings;
use strict;

use parent 'Exporter';

sub import {
    warnings->unimport('experimental::signatures')
        if $] >= 5.020;
    __PACKAGE__->export_to_level(1, @_);
}

1;
[download]