Shimano's Affordable Road Component A050 Brake Lever Can Be Replaced with ST-2300

The Shimano A050 components (7-speed) that come with affordable road bikes have shift levers that are not dual control levers but instead have downtube shifters on the top of the handlebars.

This 7-speed rear derailleur has a cable pitch that is almost the same as the 8-speed derailleur of Shimano's ST-2300, so if you replace it with the dual control levers of the ST-2300, it will work.