I’ve just verified that the logo files from you could be replaced on Xavier NX devkit with Jetpack 5.0.2 (R35.1).
Step 1. Download UEFI source
$ cd $HOME
$ edkrepo clone nvidia-uefi NVIDIA-Jetson main
Step 2. Replace logo file
$ cp frontmatec-logo-480.bmp ~/nvidia-uefi/edk2-nvidia/Silicon/NVIDIA/Assets/nvidiagray480.bmp
$ cp frontmatec-logo-720.bmp ~/nvidia-uefi/edk2-nvidia/Silicon/NVIDIA/Assets/nvidiagray720.bmp
$ cp frontmatec-logo-1080.bmp ~/nvidia-uefi/edk2-nvidia/Silicon/NVIDIA/Assets/nvidiagray1080.bmp
Step 3. Build UEFI
$ . edk2-nvidia/Platform/NVIDIA/Jetson/build.sh
Step 4. Replace UEFI binary
$ cd <Linux_for_Tegra>
$ cp ~/nvidia-uefi/images/uefi_Jetson_RELEASE.bin bootloader/uefi_jetson.bin
Step 5. Update bootloader partition only
$ sudo ./flash.sh -r -k cpu-bootloader jetson-xavier-nx-devkit-emmc mmcblk0p1