I can suppress GRUB output with terminal_output. By default terminal_output is set to "vga_text" and could be set to any of: gfxterm, spkmodem, serial, mda_text, cbmemc, audio, vga_text - only cbmemc and vga_text work.

If I set the terminal_output to cbmemc I can execute any command and return to default grub output (by blindly setting terminal_output back to  "vga_text"). 

At this point I can't boot Linux - GRUB restarts (execute blindly boot after I set root, linux and initrd) ++ and there appears to be an overflow problem in GRUB command line when having set vga_text output.

Any suggestions would be welcomed.

Thank you,

Grigore