[Lukas_Skywalker]

As an alternative, you could use the XPosed framework. It basically lets you overwrite App and System methods and classes by installing a small module. No need to modify your target apk. So you can just return true from the method that checks if the correct certificate is in use.

[ignoramous]

XposedMod is amazing but you could override methods with Frida, as well. Just that Frida works both with or without having to root the device.