We have JIRA issues with the following fields:
The release planning is based on the fix version, I suppose per default. How could it be changed to use the target version? We set the fix version when closing an issue, so it is not at all appropriate for the planning.
"Affects version" and "Fix version" are system fields in JIRA and various screens are based on them. This is logic that you cannot change.
The "Target version" is not a default JIRA field, so it must have been added as a custom field on your instance.
Instead of trying to change the concept of a "Fix version" you're better of using it as it is intended by JIRA and customising your own logic with custom fields that you add yourself. Otherwise screens like JIRA's "Releases" view will not behave as expected.
So you should use the "Fix version" field to plan the target release and update it with the appropriate version if the actual release changes. For any other kind of version info that you like, introduce your own fields.
In the "Releases" view you can click on "View in Issue Navigator" on the right side: This will show the JQL that is used by that view and it will show something like:
project = 12421 AND fixVersion = 17740 ORDER BY priority DESC, key ASC
This is hardcoded and I don't know of a way to customise this.