Is there a way to enter the JTAG USER ID code in to Xilinx Virtex and Spartan-II-based
devices other than as a BitGen option?
The only way to load a value into the "userID" register is to program the value
during bitfile generation in the Xilinx Implementation software. This can be done
from the GUI by navigating to the configuration options and enabling the User ID.
You can then enter the 8-digit hex number into the text window.
Alternatively, this can be a command line flag to the BitGen application:
bitgen -g UserID:0xabcd1234