Can I change the temperature during a challenge using the Hilo app or a voice assistant?

No.

To change the temperature during a challenge, you must use the Resideo application or the thermostat itself. While voice assistants will accept the command, they will not be able to execute it. This is a known issue with Honeywell Home thermostats. For the same reason, the Hilo app cannot control the temperature and will ask you to use the thermostat’s screen.