We can open a file with a non-default program by right-clicking the file, selecting "Open with" and browsing to the program. Once selected the program is added to the "Open with" list, for next time.
Also we have great tutorials:
for assigning a program to be the default for opening a filetype: Default Programs - Associate a File Type or Protocol
for setting the default program for a filetype Open With - Change Default Program
and for restoring the Windows defaults for many common filetypes: Default File Type Associations - Restore
Now, is there any easy way to remove the association or remove the "Open with" entries? We all make mistakes in these selections / associations and, I'm sure, like to recover from them. I have found out the underlying Registry edits, but would prefer a "GUI way".