You can't... You can use a custom home for distrobox container and place desired files into /etc/skel
For the actual command, distrobox enter overrides that and has an entry point. You can provide an environment variable of SHELL=/usr/bin/zsh for it to set the users shell to zsh
Yeah, but if I'm using vscode from another machine and want to ssh into it, it's really awkward and doesn't work well unless I directly ssh into the box