Create script to search and replace a value in an xml file

I have 2 files.

1) One is an XML file, which has product data, including article nr and one (fixed) value that needs to be replaced with another (fixed) value.

2) The second is a CSV file contains the article nrs for which this value needs to be changed.

It basically is a simple conditional search and replace.

I need a script that takes these 2 input files, then saves the new XML with a new name in same location.
Preferably this a php script, with a simple html interface with 2 input fields and a start button. So I can upload the 2 files, press start, then it downloads the new file via browser.