Repackaging is a widely used technique for modifying existing Android applications by introducing targeted changes to their code and resources. Malicious actors exploit it to distribute malware, commit plagiarism, and exfiltrate sensitive data. Although often described as a straightforward process, requiring only that an app be downloaded, decompiled, modified, and redistributed, its practical use in research contexts reveals a more complex reality. Existing work frequently overlooks why certain repackaging attempts fail, as well as the potential impact of repackage-proofing mechanisms embedded within apps. To address this gap, we present InstruMate, a novel approach for systematically assessing the repackaging resilience of Android applications. InstruMate progressively escalates from simple modifications—such as altering the app’s signature—to more complex interventions targeting code instrumentation. Each modified version is rigorously assessed against the original using novel health-check procedures that reveal discrepancies in the user interface and execution behavior. We demonstrate this approach, by evaluating the resilience to repackaging of 156 highly popular apps obtained from the Google Play Store (including WhatsApp Messenger, LinkedIn, Roblox, TikTok, among others), each exceeding one billion installations worldwide. The results reveal that 86% of the analyzed apps are non-resilient to the most basic form of repackaging involving only a signature change; 81% can be modified to enable execution in debug mode; and 83% exhibit no resistance to superficial appearance modifications. Beyond these surface-level changes, more sophisticated transformations using black-box static and dynamic instrumentation show that 65% of the apps remain susceptible to code tampering. In contrast, 11% of the apps in our dataset actively resist repackaging through explicit user warnings or runtime exceptions that abruptly terminate execution. We further trace several of these defenses to specific anti-repackaging mechanisms integrated within the analyzed applications.