I wonder whether it works to crate a form in a landing page to modify tables other than profile table in ACS.
I copied the OOB landing page template and chose another targeting dimension than profile in my copy. Then I created a landing page using my template and I tried different reconciliation keys and parameter mapping. Nothing seems to work. When I go to the testing page and choose an entry to modify, I end up immediately on the error page.
Is there any way of modifying other tables that profile from a form in a landing page?
With the current ACS version this is not doable or better to say that the feature is not available.
You can use a landing page to only modify profile or a resource directly linked to profile.
Any disconnected custom resource will have to be modified using a new feature coming out in May release. It will allow you to pick the details for custom resource in a landing page. This landing page will be able to call a custom workflow containing external signal activity. LP will pass on parameters to this external signal which can be used to update the data in your custom resource.