Remove and add data based on condition

Option 1:

Instead of loading files, you could explore sharepoint folder as a source ( https://learn.microsoft.com/en-us/power-query/connectors/sharepointfolder). The folder will have all your xls files. Say tomorrow you generate Orders_14102022.xls and save it in the sharepoint folder. The data will automatically come in Power Query since the new file is in the sharepoint folder.

Say you want to make a change on Orders_29092022.xls. You open Orders_29092022.xls located in the sharepoint folder and make the changes or overwrite with the new Orders_29092022.xls. Those changes will be reflected in power Query as power Query will always refresh by loading all the xls files located in the Sharepoint folder.

Only con of this is when you're using Sharepoint folder and a large number of xls files, the refresh time becomes very long. Another alternative below.

Option 2: 

Create a Consolidated file. Where all the 800 files are appended into one master excel sheet. Then create a power automate or Robotic Automation flow where everytime a new file is generated, that the data from that file and copy pasted it into the master file. 

If you want to make a change on a previous date, let's say 29092022, manually open the master file, filter out the 29092022 data, delete them and paste the new one in.