[otrs] Obligatory field / MIME types for attachments

Hi, currently I'm facing two problems in otrs-2.1.7: 1. I'd like to define the "Time units (work units)" field, when editing a ticket/note as an obligatory field, so that you're forced entering a value in this field. If possible, I'd like to be able restricting this to specific queues or customers. Any ideas how this could be done? 2. When adding attachments (i.e. Cisco Configuration dump, GnuPG Public Key file) to a ticket, the attachment isn't added. Instead, "*invalid" is displayed. How can I disable the MIME check completely? I think I don't need this feature at all. Thank you! Regards, Elias P.