How to edit fields' values in the hook_node_load function?
I'd go with entity_metadata_wrapper(), see this blog post for more info on that.

$node = node_load(323);
$wrapper = entity_metadata_wrapper('node', $node);
$wrapper-&gt;title = 'New title for the node';
$wrapper-&gt;save();


It works for any property: title, fields, author, etc.