I've been simplifying Mantis by removing bug status values and access levels. To do this, I've had to add statements to config_inc.php:

Trim "acknowledged" and "confirmed" from bug status values

$g_status_enum_string = '10:new,20:feedback,50:assigned,80:resolved,90:closed';

Trim "updater" and "manager" from access levels

$g_access_levels_enum_string = '10:viewer,25:reporter,55:developer,90:administrator';

I'm impressed at how smoothly Mantis adapts to this, but many people would be daunted by even this much coding. It's reasonable to require editing code when someone's adding new values. However, it seems to me that it should be simple to remove and/or rename them.

Suggestion: have a GUI page that lists all defined bug status values, access levels, resolutions, priorities, and severities. Each item could be enabled/disabled (and perhaps even renamed). You wouldn't be able to re-order or re-number things, but simple solutions could be configured simply.