You can certainly save "models" in DPS. This can more or less be done 2 different ways.
1. Save the DPS workspace once you have completed your monthly project. The next month, open the project, and change the source file location to the newest file. That will refresh all work with the new data.
2. You can also export your change history from a completed project and import it into a new project which will apply all of your edits automatically.
I hope this helps, reach back out if I have misunderstood your question.
Just to add to Austin's excellent comment.
Don't forget to save the Workspace if changes have been made that you wish to keep!
Also I think the concept for Excel (as a database in Classic) is that these days it expects to work with defined areas - so a Table within the Excel worksheet rather than a specified number of lines to skip. Normally one would just load the file and filter out any unwanted lines - which is potentially a more flexible approach than needing to specify a specific number of lines that might change at some point.
For some real fun in your situation as the developer with users to keep busy, take a look at the Data Load into a DPS workspace based on a "Monarch File". That means a model or, better, a project.
You should get pretty much everything from the Classic model except any modelled filters and sorts (currently). Lacking those is not great hardship given DPS functionality.
You end up with a Load Plan to which you can then added changes and of course filters and sorts as required.
Better yet, new source files can be added via direct drag and drop onto the Load Plan. (V14.3)
If you have yet to investigate that functionality I would heartily recommend it to you.