The 2017 Form 5500 software will be made available around the first week of January, 2018 or so.
In the meantime, if you do need to file a short or final year filing, we suggest the following in lieu of overriding existing plan data:
Once you have used the 2016 Form 5500 for one plan, you may add a second plan under the same company and prepare the second filing (for 2017) on the forms under the second plan. Note, you may want to alter one of the plan name's slightly to differentiate between the two plans in your plan drop down box. You will want the plan names to be the same on the actual forms, however. Using a second plan will maintain both filings.
To bring your 2016 information into the filing you will complete for 2017, you will first need to go to the "Form 5500-2016" screen of your 2016 filing, click on "Upload and Download Center," then select "Download Full Filing XML" and save this file to your computer. You will then need to go to the "Form 5500-2016" screen of the plan for which you are completing your 2017 form, click on "Upload and Download Center," select "Upload XML," check the boxes that correspond to the form/schedules included in the filing, browse for the XML file you have saved to your computer and then click on "Submit." Once you return to the "Form 5500-2016" screen, you should see the information from your 2016 filing, which you may then update with your 2017 information.