you can try modifying reset_global_scope https://github.com/vinx13/tvm/blob/79a1aaf693feddf1d9835779d7eb587ac0eb21df/python/tvm/autotvm/env.py#L35 and registering your custom data types there, which will be sent to worker processes.
If your custom data types are registered in cpp side, it will be available in worker processes and there are no actions needed