With the on prem version of Jira, you could customize the changeset text posted to the custom Jira field using the jira-config.properties file, e.g:
plastic.diffchangeset.url=plastic://showchangeset=cs:$changeset$@br:/@$repository$@$server$
plastic.formatdata={{html}}<a href="{5}">{0}: Changeset {1} ({4})</a><br/>{{html}}{7}\n
This (for us) was much better than a list of every changed file. How can you do a similar manipulation with the Cloud version of Jira ?