Can I change employers while holding a subclass 494 visa?

Because the subclass 494 is employer sponsored, your right to work is linked to your sponsoring employer. You are not free to simply move to any job.

To change employers, the new employer normally needs to be an approved sponsor and lodge a fresh nomination for your occupation, which must also be located in a designated regional area. Working for a new employer before these steps are completed can breach your visa conditions, so the transition needs to be managed carefully.