Since Bugzilla 2.20 RC1, legal values for Operating Systems, platforms, bug priorities and severities can be edited from the User Interface directly. This means that it is no longer required to manually edit localconfig. Starting with Bugzilla 2.23.3, the list of valid resolutions can be customized from the same interface. Since Bugzilla 3.1.1 the list of valid bug statuses can be customized as well.
Editing legal values requires "admin" privileges. Select "Legal Values" from the Administration page. A list of all fields, both system fields and Custom Fields, for which legal values can be edited appears. Click a field name to edit its legal values.
There is no limit to how many values a field can have, but each value must be unique to that field. The sortkey is important to display these values in the desired order.
Legal values from Custom Fields can be deleted, but only if the following two conditions are respected:
The value is not used by default for the field.
No bug is currently using this value.
If any of these conditions is not respected, the value cannot be deleted. The only way to delete these values is to reassign bugs to another value and to set another value as default for the field.