But its only capable of defining custom bug check code and 4 params, if you want to print custom description (text) on BSOD screen, i guess you need to go lower in kernel, probably hook something underneath KeBugCheckEx rountine.
I think that Windows gives the same description for all bugcheck. The exception may be name of the driver that probably caused the problem, and a string value for the bugcheck code (i.e. IRQL_NOT_LESS_OR_EQUAL). These string values are defined in ntoskrnl.exe or some other kernel file, if I remember correctly.