It is possible that the HK Authorities are using JAR/EASA based material.
If you go to the UK CAA website and search for CAP 698 you will find the performance manual that is used for the JAR/EASA performance exams. This book is based on an early version BOEING 737 with engine flat rated to ISA +15 degrees Celsius.
If you open the PDF and go into pages 65, 66 and 67 you will find tables for the V1, VR and V2. These tables are based on balanced take-offs, with no stopway or clearway.
On page 65 you will see a table that allocates letters A, B, C, D, E or F for increases in temperature or pressure altitude.
On pages 66 and 67 you will find tables for various conbinations of temperature/PA, weights and flap settings.
If you select one of these tables and pick a fixed weight, then move from left to right across the you will see how V1, VR and V2 vary with increasing temperature or pressure altitude for this aircraft undertaking this type of take-off.
In many cases there is no change until you get to the high temperatures.