SMS intercepted and edited before arriving?
Technically in Android you can alter SMS stored, so you can modify, them after received, and before presented to the user. Of course a malicious application can hide a received SMS and delete it before the user knows it.

About a SMS modification before sent, no you can not, but you can modify the stored copy in your phone just after it has been sent. With rooted phones it could be possible if the intercepter app has root permissions.

In Android KitKat and up only the main SMS application can perform this kind of tasks.