Yes - You can change the language without re-loading the OS - as long as your english is good enough to get to the language section to change it.
Even if you did need to do a 'full factory restore' (tapping F11 on boot) and choose spanish from the options during setup, all the omen drivers / utilities will be there already. That's part of the HP restore image.
And finally, in the event you can't use the HP FFR, you can also install stock Win10 then download the drivers and apps that came with your PC from the HP website.
You don't need to worry about the Windows license, as it's a digital key injected in the BIOS. You can install / re-install Win10 as many times as you like on this unit. Windows will automatically 'activate' itself when the unit is connected to the internet.
Hope this helps.