delete variable or modify a variable type
You should be able to remove or modify a variable from the workflow variables menu. You can currently delete a variable, but only after ALL references to the variable have been removed from the workflow, which is tedious.
I understand that this COULD result in workflow functionality breaking, but I think my below potential solutions would thoroughly address this:
Only delete/modify IF the change does not break the functionality of the workflow. As an example, perhaps it made more sense to store some string data as a "single line of text" instead of "multiple lines of text" for use in an email notifiaction. making this change wouldn't break any functionality if it was only included in a few email tasks. To prevent users from deleting more than they think they are, a warning could be presented to the user before deleting/modifying, something like "Warning, this variable is referenced in the following actions. changing/removing will not break the functionality of the action, but be aware that it is included in them: <list of actions>"
delete/modify and mark actions that were 'broken' by the change as needing configuration. Again, the user could be warned that the change would NOT break functionality in a list of actions, but that it WOULD break functionality in another list of actions.
provide tool for more easily deleting references to a variable. for instance, provide a list of links to the references found so users can quickly go to them. Also, some type of functionality that could bulk detele variables that are "Safe to delete" would help. This process is more manual, but still would be easier than current solution and should be easier to implement.
While I would prefer a built in solution as well, there is a workaround at least for the case SinngleLine -> MultiLine:
1) Export your workflow
2) open the nwf file and find the first occurance of the variable you are looking for.
3) find the ControlType property for it and change it from "SingleLine" to "MultipleLine" and save
4) import the nwf