Magento has quite good flow when order is places and in most cases Order statuses and states would be properly assigned. There are cases where that is not enough and store owner would like to assign/change order status at will without following flow rules.
When you open order view in Magento admin, under ‘Information’ tab there is ‘Comments History’ section in which you can add order comment and change order status. Order status is changed by selecting value from ‘Status’ drop-down, however values that are displayed are determined by settings under System->Order Statuses.
This can be modified with one little change allowing store admin to see all order statuses and set them at will.
All changes that will be made in one single file , but as always it is good to create a backup file just in case that you want to restore things to default.
Open in editor file:
and find line #34 and code:
<?php foreach ($this->getStatuses() as $_code=>$_label): ?>
change it to:
<?php foreach (Mage::getSingleton(‘sales/order_config’)->getStatuses() as $_code=>$_label): ?>
save file and that is it.
Now when you view order in Magento admin, all order statuses will be available in ‘Status’ drop-down and you can set them as you like.