Add metadata to custom field, custom app

We find metadata to be interesting and helpful. But the metadata is a bit hidden within the comment and it cannot be shared to another application (e.g., Jira) because it is not a field.

So our goal is some combination of the following
- modify the value of a custom field, named 'Metadata' and would have a specific Field ID
- upon ticket creation, the field would receive the metadata value(s)
- if for some reason the field already holds a value, do not overwrite
- upon subsequent edits to the ticket or comment additions, do no change or modify the field

The metadata values of interest:
metadata.system.client
metadata.system.ip_address
metadata.system.location

And the value written to the field would look something like:
Browser Client: {browserClient}
IP Address: {ip}
Location: {location}

We've found a custom app and modified it slightly to better suit our needs. But the app just appends the metadata to a comment rather than to a field. And the metadata is added to each and every comment. We just want to put the first comment's metadata into a field and that's all. The custom app is here and it works (but with the limitation mentioned):
https://github.com/eric-at-zd/metadata-writer

Is anyone up to create a version of the app which modifies a specific field? If we had the code, we could generate our own version of the custom app which modifies our specific field (by Field ID or by field name).

Thanks!