Audacity’s File>Edit Chains feature, allows the user to apply multiple effects with customized settings, as well as ‘Tracks’ menu functions (e.g. Stereo-to-Mono), to a batch of sound files.
Audacity’s File>Export Multiple feature enables common metadata to be inserted to a batch of sound files.
Is there a way of combining ‘Chain’ and ‘Export Multiple’, so that effects processing and common metadata allocation can all be done in one go, and if not, why not? 
Export Multiple is not currently supported by Chains.
Why?
The underlying mechanics of Chains is a simple list structure. It was originally introduced to provide automation for a specific task of cleaning up and compressing short speech files (part of a long abandoned “Clean Speech” project that one of the developers had a personal interest in).
Since that time, the Chains feature has been greatly expanded to support most effects, and a couple of additional export options, but it is still limited by the underlying linear “list” processing of single files or a linear chain of effects on the current project.
In order to support more advanced features such as editing with time selections, conditional processing, multi-file editing, recording, and so forth, requires a more flexible scripting system. The old “Chains” mechanism was never designed for the job, and frankly isn’t up to the task. There is however a new scripting feature under development. It will probably be a few releases before this is ready for public release, but you can get a sneak preview of some of the work being done here: https://alphamanual.audacityteam.org/man/Automation_Reference
Got it. Thanks again Steve.
For the moment I guess I’ll just have to run the two batch processes separately.
All the best! 