Changing a Template within Files used to import data from a Folder

Folks - 

For the last ~18 months I have built out an extensive data model utilizing many different tables. Some of the tables are being generated by excel files saved within a folder. Utilizing the folder import option and intilizing the model was very helpful. I refresh everyday, and obtain the new data for the day. However, I not have a need to add an additional column in the excel file.

In the past when I wasnt so far ahead - I changed every file to include this new column and simply set up the query from scratch. I'm sure this is a more effecient way to simply add a new column in my excel files and alter some confirgurations within Power BI/Power Query to pick up the new columns without having to edit all the other files to also include this new column. 

When I'm pointing to a single file - I am able to make changes within the advanced editor. Here, I notice Power Query has created a "Transform Sample File" which I bleieve is what Power Query is sampling to store all the 'Applied Steps'. Correct me if im wrong.

I'm simply adding a new column to the excel file. Can I somehow have the power query recognize this new column without everything else breaking?

If more information, or detail is required, please let me know. Thanks!