Updated to address Roy Johnson's concerns below

sub insertAfter{
    use List::Util qw[ first ];

    my( $aref, $before, $insert ) = @_;
    my $first = first{ $aref->[ $_ ] eq $before } 0 .. $#$aref ;
    return unless defined $first;
    splice @{ $aref }, ++$first, 0, $insert;
}
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