This document explains why the Status Lookup field may not be changed to a Dropdown list despite the SelListCacheMax parameter in NX_ROOT\bopcfg\www\web.cfg file being modified.
If the Multi Tenancy option is installed, the Status field will always show as Lookup field. This is because there is no way for Service Desk to determine how many values will be listed in the Status field based on the Tenant that the user selects. Once the ticket is saved and Tenant field filled in, the Status will always be displayed as a dropdown. This is working as designed.