One of the first possibilities to modify SPIP’s behaviour is to copy one of its files from
ecrire/ into a folder with higher priority — a plug-in or
squelettes/ folder, for example — while preserving the folder hierarchy.
Thus, one could modify the way in which SPIP manages the cache by copying
squelettes/public/cacher.php and then modifying this copy. It is this modified copy which would be loaded by SPIP as it — being in
squelettes/ — has a higher priority than the original.
This technique must be used with full knowledge of the facts. While this technique is very powerful, it is also very sensitive to changes in SPIP. If you use this method, you may find it difficult or impossible to upgrade your site to future versions of SPIP.