Are you using the developer chrome extension? i haven't used this functionality but seems like you can use it to search for fields by name, returning a list of the modules that contain that variable and also a swap variable functionality.
Or what we have used but not a very elegant solution, you can export your scenario as a JSON file, then open it in a text editor like notepad++, use find + replace All to find the old field name and replace it with the new field name. Save it and import the updated file back into Fusion.
Thankfully the ability to change the field label and leave the field name the same in Workfront has been a life saver for changes like this.