Hello Chi and kybernator,
chi wrote
just a "yes" doesn't help the one who asked the question, does it?
It's just that there are some ethical aspects involved in antedating...
For the default template, displaying the modification date is handled by tpl_pageinfo() in the file <DOKUWIKI>/inc/template.php. Some templates (mine is based on dokucms) have their own version (look in <DOKUWIKI>/lib/tpl/<YOUR TREMPLATE>/main.php).
replace
$date = strftime($conf['dformat'],$INFO['lastmod']);
with
$date = strftime($conf['dformat'],$INFO['lastmod'] -24*3600);
Have a good weekend!
Hansel