How do I change the file association to a program with the same name in Windows 7?
You could always make the change in the registry under:
HKEY_CLASSES_ROOT and HKEY_CURRENT_USER\Software\Classes
But I would highly recommend the program Types from Sourceforge for control over all parts of the association process.
You can try free Default Programs Editor. I have a good experience with it.
I would use Creative Elements Power Tools, specifically the "File Type Doctor".
http://www.creativelement.com/powertools/#download (to download)
http://forums.techarena.in/tips-tweaks/989159.htm (for a screenshot)
This has the advantage of looking almost exactly like the XP file association area, so you would be familiar with it.