Replacing text in files

This small .exe program will accept as input from me a folder (found with some 'Browse' button), similar to the one I am attaching, and a number, let's say 2010. It will then check every file in the folder and replace 2010 _wherever_ it is encountered (i.e. both as a file name but also IN that file) with something else, but PROVIDED 2010 is followed by a _letter_. That 'something else' will be the last digit of my input number (2010 in our example), which is the digit 0 of course. Thus if in the folder there is a file named say [login to view URL] it will become hg20m21Apr22Apr. Also IN that file if there is, say, hg52010j21Apr22Apr somewhere it will be hg50j21Apr22Apr. But if we had hg52010$[login to view URL] it would _stay that way_, because 2010 is followed by a symbol ($) not a letter! Also if we had inside the file hg5201021Apr22Apr it would STILL remain intact, because the 2010 is followed by a number (number 2), not a letter. All files in the input folder are of the same form, as you can see in the attachment. So the program doesn't have to search much in those files. Actually I don't mind if it only searches (and replaces) at the first 'column', since the other columns only contain dates or numbers, no text. The program must transform a folder like the attached and all its contents in a matter of a couple of seconds.