Would anyone know if it’s possible to convert the interrupt pin from active high to active low?
The AS3935 datasheet does not describe the IRQ pin as being configurable for levels; it states that it will pull-up the pin high when an event occurs and will set it back to low when the register is read.
Put a hex inverter chip on INT?
Would a 74HC04 work for this purpose. Will it preserve the required voltage for 3.3V logic boards?
That should work. In keeping with SFE’s offerings, the following will also work: https://www.sparkfun.com/products/13952
The reaction time of the 74HC04 seems so much more tempting than the Schmitt Trigger.
Keep us posted on how it goes, whatever you decide to use. I presume by reaction time you mean how fast it responds from input to output; since this interrupt is not measured in usec I don’t think the device you choose makes much difference (could be wrong though).