By "personalizing a downloadable" I mean: Embedding (some of the) customer information into the downloadable product itself. For the sake of this discussion, assume that the actual merge of customer information (passed from Zen Cart) into a file has been solved (by an external program, a servlet or by a simple PHP file append).

The challenge (for me) now is how to implement this in Zen Cart, in the most correct way.

By "most correct way" I mean: Minimum (or no) hacking into Zen Cart's core files. That is, ideally requiring only observer(s) and/or using the override system, without requiring to hack includes/modules/pages/download/header_php.php as described in DrByte's tip from may 2007.

Is this possible?