Hi there, if you need to replace the Add to Cart button with the Pre order button and clearly notify customers that particular products are available for pre order please take a look at this module: http://amasty.com/magento-pre-order.html.
- easily customize Pre Order button and place it on product and category pages;
- specify any additional notes that will be placed on a product and shopping cart pages (eg. “Available in 14 days")
- create warning messages to remind customers that the product is pre ordered
- easily manage pre orders on order grid;
Take a look at the screenshots below to get a better idea of the module’s functionality: