Are there some screenshots you could provide to show what you are trying to do? from how I understand, you are trying to change the dropdown of an input within a set of dashboards. however I would just name the dropdown as required for each dashboard. If you need the name to change, then control the value with a token, depending on how you want to show it.
The splunk dashboard examples app may have some content within which should help (https://splunkbase.splunk.com/app/1603/)
