web content "mining" using supervised learning tequniques
In short, this is probably difficult.

Your question is not fully specified, since you did not write the details of the data you are parsing and since estimating the possible changes to it is a matter of guesswork.

Once this web site changes format, then if we assume that the products remain the same, you are essentially looking at supervised learning task: given a list of known product web pages, make an "extractor function" that outputs the desired field.

If you are lucky and all the product pages are identically structured then this problem might be quite easy. You simply need to identify the path to the node of the HTML in which the desired information lies. On the other hand, if the web pages have a varied structure, or no structure at all, then the problem may be much more difficult.

There are some academic works in these areas, but don't get your hopes up. Look for the keywords "automatic web extraction".