Custom Commands - file editor - run as different user possible?

Ubuntu 16.04, Webmin 1.89.

I have a bunch of LXC commands in the custom commands module to administer some LXC container configs. Works great except for the file editor. It seems to open files as root. But since LXC is locked to a user folder and wont install as root, I am unable to edit files on LXC containers. Namely my host server needs to be able to edit the netplan config on each new container. I can pull the file and save to the host, edit the file, and push the file back to the container in three separate commands but I can not use the file editor with the “run before and after commands” to do all 3 at once because root is the user running the file editor command.

Is there no option for “run as a different user” for the file editor like there is for the commands editor?