To disable Steam integration functionality, delete the configuration Assets/StreamingAssets/EOS/eos_steam_config.json before building.
At runtime, the sandbox ID can be overridden with the launch argument -eossandboxid=<id> and the deployment ID with -eosdeploymentid=<id>.
To specify deployment IDs in this case, Sandbox Deployment Overrides can be added in the plugin config editor to define sandbox-deployment pairs, which will override the deployment ID when a given sandbox ID is used.