如何在netsuite中使用nlapiSetFieldMandatory（fieldname，bool）

Can someone help me to use this function nlapiSetFieldMandatory(fieldname,bool). I try change the field from mandatory to non mandatory using this function. but it didn't work. My friend told me. The operation works in the debugger and also for custom fields. However, because the field im using to change is an system field there is an internal guard call that blocks the change. When you are in the debugger it is treated as "internal". Can some one help me or explained this. Appreciate the help. By the way in using javascripts client script. Thank you,Can someone help me to use this function nlapiS