The Win32_ComputerSystem class is indeed used by Windows to identify the hardware configuration of your computer, including whether it's a laptop or a desktop. However, changing the value of the PCSystemType property in the registry may not be the best solution for your problem.
Modifying system registry settings can be risky, and it's generally not recommended unless you fully understand the implications and have a backup of the registry. Additionally, changing the system's classification from laptop to desktop may have unintended consequences on certain power management settings and drivers that are specifically designed for laptops.