Hello Daniel,
Thanks a lot for your interest in using MoveNet! You are right the MoveNet releases are currently not fine-tunable. But the model implementation is actually based on the Tensorflow Object Detection API 7 so you should be able to access the model code and modify it for your own purpose. As mentioned in the documentation, the MoveNet model is based on CenterNet with some modifications in the postprocessing logics and ops re-write to boost the performance. The closest model architecture can be found here 25. You can also find some example training configs in the /models/research/object_detection/configs/tf2/ folder.
I’d recommend you to start with the above codebase and modify from it. There are a few internal modifications which have not been released yet. We are still working on it and will let you know once it is there. Thanks.