you can change the HOR for 2020.
While it's easy to change your HOR with the military, that does not make it legal with the state or the IRS. Every state has their own residency requirements, and just being stationed in a state under military orders does not in and of itself meet the residency requirements of any state.
See https://www.caltax.com/wp-content/uploads/2018/03/NonresidentsONLINE.pdf page 50, "California Military Personnel Assigned to Stations Outside California"
Also, see https://www.dcms.uscg.mil/Portals/10/CG-1/PPC/guides/gp/spo/Deductions/State_Tax_Withholding_Excepti... for what you need to do via your CAC login to stop state tax withholding. Any questions on that, contact the base pay center (Called it CBPO in my day. Don't know what they call it now) or base legal.
If you filed a resident return in prior years and paid CA taxes, then you *NEED* to contact base legal for help with "un" doing that and filing a non-resident state return to get withheld taxes refunded. It's not as simple as amending your already filed and processed resident state tax return.
