How to Use "Rules for Quantity Range Status"
If you want to use this feature in Custom Stock Status, please follow these steps:
1. To activate the rule, please go to: System > Configuration > Custom Stock Status
2. On General tab find "Activate rules for Quantity Range Status" and switch it to "YES"
3. Go to: Catalog > Attributes > Manage Attributes > Custom Stock Status Qty Rule
4. On Manage Label/Option tab create some Options for the attribute
5. Go to Catalog > Attributes > Manage Attributes > Custom Stock Status
6. On "Quantity Range Statuses" tab specify Statuses and Ranges for each Rule
7. Now you are able to edit rules for each product. Go to Catalog > Manage Products > Choose any product and specify the rule for it on the general tab.
Make sure to switch "Use Quantity Ranges Based Stock Status" to "Yes"
See more details on Custom Stock Status page