Change cboot boot logo (L4T 28.2)

Hi,
I followed your steps but when I enter this command:
sudo ./flash.sh -k BMP --image ./bootloader/bmp.blob jetson-xavier mmcblk0p1

I get this error: Error: Return value 8
Command tegrarcm_v2 --download bct_bootrom br_bct_BR.bct --download bct_mb1 mb1_bct_MB1_sigheader.bct.encrypt --download bct_mem mem_rcm_sigheader.bct.encrypt
Failed to flash/read t186ref.

Also, I tried this on jetson TX2, and the logo changed. But, after my logo nvidia logo appears on the screen.
Is it normal? Can I remove Nvidia logo completely?