If you want to change your Origin afterwards but want to keep your progress except HWS DNA, you can fly to the Origin Quadrolith on the ECC Planet in the Homeworld PvE System.
Just stand in front of the LCD screens telling you how to do it and type the proper command.
Note:
- You will lose all of your HWS DNA on change
- You have to leave your faction for a change. Make sure to set your structures to private before you change your origin!
Bonus: Inside the Origin Quadrolith there are couple of easter eggs and a side mission for farming HWS DNA.
Be careful of the defenders though. 
