is there a way to affect a app/game with another app/game like add stuff or take away stuff or change certain scripts? to clairfy its my own unity apps/games im not trying to hack anybody’s app/game
Sure. Using a webservice to communicate.
For example… If some user earn a coin in the AppX then he/she can use that coin in the AppY.
The only thing that you need is update some database where both can access and share informations.
On Android, Google states that using the same Key to sign your Apps enables the Apps to share data between them.