Skip boot menu by readin status from gpio, eeprom, uart?

Hello everybody!

In siabios there are functions romfile_loadfile romfile_loadint for reading values from cbfs. 
Is it possible to somehow write new data to these files from SeaBios? That changes must be saved on the SPI flash with BIOS.

Also interested in adding gpio read functions to the siabios or eeprom read (smbus) functions.

The task is to show the disk boot menu only when a jumper is inserted. Or when reading a specific value from eeprom. 
The default drive boot menu should not be available.

Maybe reading from the UART port can be done?