I believe most of the functionality needed is already available as some TextMesh Pro users have already implemented their own system to batch generate font assets. There should be a few posts about this on the TextMesh Pro user forum.
Obviously this is where having access to the source code is nice. Unless you are locked into a previous version of Unity, the version of TextMesh Pro for Unity 2018.1 and up which is available via the package manager is provided with source code. If that is an option for you, be sure to review the following post and upgrade procedure.
Separate from all that, adding specific API functions to do exactly what you describe is in the plans.