How to toggle a pin in Harmony framework for a pic?
There are two ways of configuring timers in harmony v2. 

i.e. Static or Dynamic

For static timers you need to add your handling code into the system-interrupt.c file timer handler. See here

For dynamic timers you can specify a custom handler in your application code. See here. See 'Creating the ISR' and 'Registering the ISR' sections.

I would use the harmony timer system service, see here, which is a bit simpler implementation and similar to dynamic implementation but might result in less accurate timing due to extra software handling. 

LATGINV is not typical usage.

There is pin toggle example code in this example.

To toggle your LATG 0 pin with harmony you may do the following

Initialization

PLIB_PORTS_PinDirectionOutputSet(PORTS_ID_0, PORT_CHANNEL_G, PORTS_BIT_POS_0);


Toggling

PLIB_PORTS_PinToggle(PORTS_ID_0, PORT_CHANNEL_G, PORTS_BIT_POS_0);


The microchip developer help is quite in depth and I'd recommend reading