Advanced HID function, Arduino Leonardo/Trinklet/Attiny85 with Microsoft Excel

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Hello, I need guidence building a program which will be connected via USB (V-USB/32U4).

Functionality required:
- When I press a hardware button connected to a pull up line, to increment a value in Excel by 1 (I have a Macro button when pressed increments the value by 1)
- Most importantly it needs to operate if Excel program is minimsed or open in the background.

Basically I don't need the usual HID command list to simulate pressing a button, since for this you have to have the program you want to manipulate selected/maximised.