for tracking purposes, I want that the URL, which appears on the facebook stream after an \"like-action\", is slightly different from the URL the user actually liked.
You can't do exactly what you have requested, but you can still add an arbitrary tracking parameter (especially useful for analytics purposes). Facebook recently added a ref parameter to the fb:like
element for this purpose. It's up to you to decide how you want to stuff various bits of information into that single parameter and then parse fb_ref
whenever it's included in an incoming URLs.
Example
Place the following element on your HTML page:
Users clicking the link from Facebook should be directed to:
http://example.com/test.html?fb_ref=144141&fb_source=home_multiline
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