@황인호 It isn't required to use voxl-modem to interact with the modems if you'd like to do a custom config.
In your case, I'd recommend using voxl-configure-modem with the quectel option to handle Quectel bringup and then creating a custom script / service file (or modifying the existing one) to handle doodle bringup.
Although doodle bringup is very basic, if you follow the code path here in the startup script: https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-modem/-/blob/master/scripts/voxl-modem-start#L99
it monitors the eth0 network interface and if the IP address isn't what is specified in the config file then it assigns said IP address. This could be broken out into a different script