Different ways to import parameters

There are multiple ways how parameters can be imported from some other model or checkpoint.

Custom script generating new TF checkpoint

This is the most flexible option.

Config option preload_from_files

Layer option custom_param_importer

Layer init options (forward_weights_init and others)

This uses get_initializer and can in principle use any initializer, or even custom initializing code, which could import other parameters from a checkpoint or elsewhere.