It's quite simple. Open up the post processor and edit these lines:
var coolants = [
{id:COOLANT_FLOOD, on:8},
{id:COOLANT_MIST},
{id:COOLANT_THROUGH_TOOL},
{id:COOLANT_AIR, on:8}, <------- add the "on:8"
{id:COOLANT_AIR_THROUGH_TOOL},
{id:COOLANT_SUCTION},
{id:COOLANT_FLOOD_MIST},
{id:COOLANT_FLOOD_THROUGH_TOOL},
{id:COOLANT_OFF, off:9}
If you don't want to edit the post processor, there's no reason why you couldn't just leave it set to "Flood Coolant" in Fusion, since it's going to spit out the M8 anyways. Just know that M8 is the code you need on the machine side of things to activate your air coolant. Or, just change the post to whatever you need.
If you DO edit your post, save the post processor locally and set your Post dialog to use that one instead of the generic one from the library.
Seth Madore
Customer Advocacy Manager - Manufacturing