As far as I'm aware, it's not possible to change the caching values
for children of the parent templates. The output is cached for a
display()/fetch() call and all its descendants.
Theres no reason why you have to only have the one template and
include everything in from there.. you can do it like this:
Code:
<?php
$smarty->cache_lifetime = 10000;
$smarty->display('header.tpl');
$smarty->cache_lifetime = 30;
$smarty->display('banner.tpl');
$smarty->cache_lifetime = 1800 + $randomness;
$smarty->display('content.tpl');
$smarty->cache_lifetime = 10000;
$smarty->display('footer.tpl');
?>
I do all my pages like this for the fine tuning it allows.