Adding an extension to series of file names

[MGHSJ1961]

I want to add an extension such as .jpg or .tif to each of the file names in a series of cells in Excel without having to click on each cell and paste the extension in each of the cells. It gets very tedious 200-400 times. Excel easily builds the sequence of numbers by dragging the corner of a cell sequence. But I can't find a way to add the same set of characters to the end of each file name in a long sequence. Is it possible?

[#2]

As a short term fix (assuming this isn't something you have to do every day, in which case a macro might be needed to automate what I'm going to tell you...)

In the column next to the cells in question, enter this formula
=CONCATENATE(A1,".jpg") OR =A1&".jpg"
In place of A1 in that example, just place whatever your top cell reference is.
Copy this formula down next to the whole column.
Then highlight your new "complete" names.
Copy
Put on top of the originals and select "Paste Special" and select "Values"

Then you can erase the formulas; they were just temporary to accomplish that change.