Replace Workbook in Folder Without Overwriting Certain Data

replacing the workbook already there, but not the changes made to that existing workbook.

This is such a contradiction that I can only assume that I don't understand the question. Replacing a workbook replaces the workbook. Perhaps more detail would help.

Let me try to paint the scenario that you may be trying to describe.

You copy a file from the Internet. Let's call that Version A. You make edits. You save it in your folder. Let's call it Version B.

The next day, you get a new version of that same workbook from the Internet, and also edit that new version. Let's call that Version C. Version C has your new edits, but not the edits you made yesterday in Version B. You want to merge yesterday's edits in Version B into today's edits in Version C, and then save Version C, replacing Version B.

The coding part isn't terribly hard but if I understand correctly, here is the problem you need to solve. Suppose you complete your changes to create Version C, and now you compare it to Version B from yesterday. You find that there is a cell that has one value in Version B, and a different value in Version C. You don't know if:

1. You changed the cell when you created Version B, and now Version C shows the value as it was taken from the Internet. You need to keep the change made in Version B.
2. There were no changes to this cell until you created Version C, and you can use the value from Version C.
3. You didn't make any changes at all, in any version, but the version you just copied from the internet to make Version C is different than Version A that you used to make Version B yesterday. You want to therefore use the latest value provided by the Internet, and keep Version C.
4. You changed the value when you created Version B, and you changed it to something different when you created Version C. In this case, which one do you want to keep?

To be able to deal with these cases you need to build a way into your file to track what changes you are making each time so you know what change takes precedence when there is a difference. To give more specific advice I would have to see the file, and understand just what things you change.