[otrs] customer users 250 max number

Hi, I've got more than one thousand customer users in my db but when I would like to search them in the frontend agent user interface I can view only 250 elements. I've installed OTRS 2.3.4 and I read something about this issue but no solutions. (I tried to modify the "my $SearchLimit" parameter in the AdminCustomerUsersService.pm file but It didn't work). Can anyone help me? Thanks Alessandro