A: Possibly. The official app may detect abnormal gold amounts if you link to Google Play Games. Always clear app data before switching back.
If you have the Play Store version installed, remove it to prevent signature conflicts. A: Possibly
The search for " Gunship Battle: Helicopter 3D with a mod APK for unlimited gold coins refers to but as of this writing
A: The official latest is higher (2.7.x), but as of this writing, 2.6.51 is the most stable modded release. Newer mods often break OBB compatibility. A: Possibly