User Apps crash after change os version

[iThanh]

My real ios version is: 7.1.2. Some applications/games installed on my device can only running in ios 7. When I try to hook and change os version to newer version (ex: ios 8.1), some applications can't be launch. Because this detect os version and run corresponding method that doesn't has on iOS7 SDK. This is why some applications can't be started if the higher ios version is detected.
Have any method on tweak help me to bypass this error. Thank you!