Overriding file lock for writing extended attributes

When I try to write extended attributes using setxattr() it fails with  
an EPERM POSIX error when the file is locked. Is there a way to  
override the lock and write extended attributes to locked files? For  
instance, when NSDocument saves to a locked file it will be able to  
write anyway, usually after asking the user using an alert. So how can  
I emulate this or EAs?

thanks
Christiaan