Hi Julian,
You can't really do it "easily" without getting your hands a bit dirty with code. With code, it's a snap. Now, I 'm going to provide a tiny script that does what you want, but please remember to
backup your database first etc etc so that you don't shoot yourself in the foot if something goes wrong. Not that it will, but you know, just being cautious.
Now for the code: just copy and paste this into a .php file in your Moodle root directory (the same directory where config.php is). Let's assume you call this file "resetblocks.php". Simply go into your browser, visit
http://your.site.here/moodle/resetblocks.php and it should all return to defaults.
Remember to remove this .php file afterwards; you don't want anyone else to do it when your site is operating!
The code is:
<?php
require_once('config.php');
require_once($CFG->libdir.'/blocklib.php');
$courses = get_records('course');
foreach($courses as $course) {
$page = page_create_object(PAGE_COURSE_VIEW, $course->id);
blocks_repopulate_page($page);
}
print_heading('Done!');
?>