HTML changes:

Modify "html/Search/Elements/PickBasics"  under the <select name="ActorField"> add the line
<option value="UpdatedBy"><&|/l&>UpdatedBy</&></option>
so your options for select list now:

<select name="ActorField">
<option value="Owner"><&|/l&>Owner</&></option>
<option value="Creator"><&|/l&>Creator</&></option>
<option value="UpdatedBy"><&|/l&>UpdatedBy</&></option>
<option value="LastUpdatedBy"><&|/l&>LastUpdatedBy</&></option>
</select>


LIB changes:
Modify "Tickets_Overlay.pm" :
In 
my %FIELD_METADATA = (
Add the line:
UpdatedBy       => [ 'TRANSUSER', ],

In
my %dispatch = (
Add the line
 TRANSUSER       => \&_TransUser,

Then add the sub:

sub _TransUser {
    my ($self, $field, $op, $value, @rest ) = @_;
    #$RT::Logger->error("the field = $field and op is $op and value is $value and rest is @rest");
    $self->{_sql_transalias} = $self->NewAlias('Transactions')
    unless defined $self->{_sql_transalias};
    $self->{_sql_Usersalias} = $self->NewAlias('Users')
        unless defined $self->{_sql_Usersalias};


    $self->_OpenParen;

    #Search for the right field
    $self->_SQLLimit(
        ALIAS         => $self->{_sql_Usersalias},
        FIELD         => 'Name',  ### for the Updated by in particular may changes later
        OPERATOR      => $op,
        VALUE         => $value,
        CASESENSITIVE => 0,
        @rest
    );

    $self->_SQLJoin(
        ALIAS1 => $self->{_sql_Usersalias},
        FIELD1 => 'Id',
        ALIAS2 => $self->{_sql_transalias},
        FIELD2 => 'Creator'
    );

    $self->_SQLJoin(
        ALIAS1 => 'main',
        FIELD1 => 'Id',
        ALIAS2 => $self->{_sql_transalias},
        FIELD2 => 'ObjectId'
    );

    $self->SUPER::Limit(
        ALIAS           => $self->{_sql_transalias},
        FIELD           => 'ObjectType',
        VALUE           => 'RT::Ticket',
        ENTRYAGGREGATOR => 'AND'
    );

        $self->SUPER::Limit(
        ALIAS           => $self->{_sql_transalias},
        FIELD           => 'Type',
        VALUE         => 'Comment',
        ENTRYAGGREGATOR => 'AND'
    );

   $self->SUPER::Limit(
        ALIAS           => $self->{_sql_transalias},
        FIELD           => 'Type',
        VALUE         => 'Correspond',
        ENTRYAGGREGATOR => 'OR'
    );


    $self->_CloseParen;
}