Eddie says I can change the DSDT table on my HP laptop, using the ASL Compiler.
I did this and it seemed to work.
Should I be worried about future BIOS updates?
I found DSDT defined here. This is defined in ACPI as a way for the BIOS to tell the OS how to access & configure the features that the system provides such as thermal control and configuration. The method used overrides the tables provided by the manufacturer's BIOS. It is intended for debugging and development. Future BIOS updates may be overridden as well. Proceed with caution. Keep an eye on your system's temperature readings for awhile to make sure slowing down the fan doesn't have any unintended consequences.