We do not recommend modifying the files in the downloaded C++ library, as the source code and model are tightly coupled. As you have found, slight variations in versions used to produce a TFLite file could break the build process.
If you wish to modify a model, we recommend doing so in your Studio project (you can use Expert Mode to see the Keras code). Once you have trained the new model, you can download the updated C++ library from the Deployment section. This will ensure that all functions/variables are working within your library.