To alter the vibration rate/frequency in the Diamond, I could either build a physical connection between the Dock and the Diamond or use radio frequency as a wireless communication between Arduino Uno and ATtiny85. The former would need some serious product design knowledge and would most possibly pose problems when it comes to building it, but the latter will solve the need to build a physical connection between the Diamond and Dock.
I found 2 methods for wireless communication:
The first method requires some extra hardware, an RF receiver and transmitter module, while the second one is a bootloader designed for ATtinys and ATmegas.
More about TinySafeBoot here: https://ladvien.github.io/robots/tsb/