In the context of a software company in Spain developing mobile applications with an expectation of many small updates due to changing configurations and customer feedback, focusing on being able to change the software effectively and efficiently during initial development without introducing new defects is crucial. The maintainability sub-characteristic that should be covered by the test approach during the initial development is Modifiability.

Modifiability refers to the ease with which a software product can be modified to correct faults, improve performance or other attributes, or adapt to a changed environment. In a scenario where frequent and small updates are anticipated, ensuring that the software architecture and design support easy modification is vital. This not only aids in implementing changes more rapidly but also helps in maintaining the stability and integrity of the application, thereby preventing the introduction of new defects. The focus on modifiability ensures that the software remains responsive to customer feedback and evolving requirements without compromising on quality or performance.