Is it possible only using Hive OS and Antminer firmware?
not with stock firmware. if using hiveon firmware then yes.
My intention is to install an external exhaust to reduce the noise.
How could I do this? Is there a specific code in the Hive OS prompt?
which model?
depending on the model you should see something like this, flip the switch for immersion and it will ignore fan errors
Bitmain Antminer S19 /95TH
then it will look the same as above. you can also find the setting on the ip dashboard after flashing hiveon firmware.