Unfortunately, the source code of the functions dtr_raw_sql_push and dtr_copy_data cannot be retrieved. As you mentioned, the new deployment would overwrite the existing functions, this is by design. It is recommended to create multiple functions inside one function app and deploy them at once. You can configure source control using github/git and build a CI/CD pipeline to automate the deployment process.
https://learn.microsoft.com/en-us/azure/architecture/example-scenario/apps/devops-dotnet-webapp
Hope this helps!