Well, I copied CloseParentAfterClosedChilds.pm to TestACL.pm in the same directory.
I added to Config.pm this code:

    $Self->{'Ticket::Acl::Module'}->{'2-Ticket::Acl::Module'} = {
        'Module' => 'Kernel::System::Ticket::Acl::TestACL',
    };

I modified Run subroutine of this new module in following way:

    $Param{Acl}->{TestACL} = {

        # match properties
        Properties => {
        },

        # return possible options (black list)
        PossibleNot => {
            # possible ticket options (black list)
            Ticket => {
                Priority => ["1 very low"],
            },
        }
    }

    return 1;

Now very low priority should be disabled for all tickets. Am I right? However, it isn't.
Also, I added this code to new and Run subroutines of the new module:

    open(MYFILE, '>>/var/tmp/acltest.log');
    print MYFILE "I AM IN MODULE\n";
    close(MYFILE);

However, no data in /var/tmp/acltest.log is added. So, module is just not being loaded. I'm sorry
for my being so unskilled in Perl (most of development comes in Python for me). What am I
doing wrong here?

--
regards,
Mikhail