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You can use firebase-tools as a module which would allow you to do things like deploy, or you can use the Firebase Hosting REST API directly to deploy, but in both cases you will need to maintain your own filesystem with the canonical source of truth. Firebase Hosting is versioned, and each new version must be created and populated with all of its files (you can’t just change a single file, for instance).
With a good amount of work, you could use the REST API to effectively copy all of the files from one version into a new one and populate a few small changes, but this is a rather advanced use case and will likely not be straightforward.
In many cases, it will be simpler to use a Cloud Function to dynamically serve the content through Firebase Hosting instead.