What you have read is true... it is possible that some hardware and/or software may not function and/or operate properly if you install Windows 7 on a computer that shipped with Windows 8.
HP doesn't recommend the installation of Windows 7 nor will it support the installation of Windows 7 on a computer shipped with Windows 8. HP will not provide Windows 7 drivers and suitable drivers may not be available for the hardware in the computer. Additionally, Windows 7 may not support some of the hardware or software features designed for the computer.
Create your HP Recovery Discs before modifying or changing ANYTHING.
You will need to DISABLE "Secure Boot" and ENABLE "Legacy Support" in the BIOS and save those changes before you will be able to install or run Windows 7. You may also need to confirm these changes after rebooting the first time.
Again, you will need to have a valid Windows 7 COA with an unused product key before you can attempt to install Windows 7 on this computer. Please see this HP forum thread entitled "g7 2233 missing drivers after windows 7 ultimate 64-bit clean install" for compatible drivers. Pay specific attention to the advice of lasvegaswireman and Paul_Tikkanen in that thread.
The problem with bringing back and getting something else, is that every Windows computer being sold at retail stores comes with Windows 8. The only way to get Windows 7, is to purchase a business model directly from the likes of HP, Dell, etc.
Please send KUDOs