This is the command used to flash only the ESP32 firmware:
$ meadow flash os -v 1.8.0.0 -d -k
Skipping step to flash Meadow OSConnecting to Meadow on /dev/ttyACM0
Skipping update of runtime.
Meadow StdInfo: Mono is disabled
Updating ESP
Transferring /home/alan/.local/share/WildernessLabs/Firmware/1.8.0.0/MeadowComms.bin
Starting File Transfer...
Meadow StdInfo: File received, flashing ESP32
Meadow StdInfo: Flash 10% complete
Meadow StdInfo: Flash 20% complete
Meadow StdInfo: Flash 30% complete
Meadow StdInfo: Flash 40% complete
Meadow StdInfo: Flash 50% complete
Meadow StdInfo: Flash 60% complete
Meadow StdInfo: Flash 70% complete
Meadow StdInfo: Flash 80% complete
Meadow StdInfo: Flash 90% complete
Transfer Complete, wrote 1278400 bytes to Meadow
Transferring /home/alan/.local/share/WildernessLabs/Firmware/1.8.0.0/bootloader.bin
Starting File Transfer...
Meadow StdInfo: File received, flashing ESP32
Transfer Complete, wrote 24896 bytes to Meadow
Transferring /home/alan/.local/share/WildernessLabs/Firmware/1.8.0.0/partition-table.bin
Starting File Transfer...
Meadow StdInfo: File received, flashing ESP32
Transfer Complete, wrote 3072 bytes to Meadow
Connecting to Meadow on /dev/ttyACM0
Connecting to Meadow on /dev/ttyACM1
Updated Meadow to OS: 1.8.0.0, Mono: 1.8.0.0, Coprocessor: 1.8.0.0
Done!