I don't know if it will work for 3.72 HX-2 =| but they say "applying the 1.50 kernel onto PSPs with 3.72 HX firmwares"
so it should work for all HX firmwares. (including HX-2)

QJ Wrote:Here's another bit of Sony PlayStation Portable home-cooked goodness from PSP homebrew developer Dark_Moon: a kernel add-on utility that pretty much makes the unlocking of our handhelds' fullest potential easier and smoother (i.e. applying the 1.50 kernel onto PSPs with 3.72 HX firmwares). For a better idea of what this little utility does, here's Dark_Moon himself with the release notes and the instructions:

Instructions :

   1. When you have installed the firmware 3.71 m33 and the kernel addon download this file and open MS_ROOT. Then copy the PSP folder to the root of your memory stick.
   2. Run the app, and press Square. Now the program will start to dump the addon. The dump is on ms0:/psp/game/update/km. Copy the km folder to your hd.
   3. Install 3.72 HX. Later copy again the PSP folder that contain this app to the root of your memory stick.
   4. Connect the USB (Flash0) and copy the backup done before in the root of the flash0. Run de app again and press X. It will copy the reboot150.prx and all will be done!

As always, please do take care while using this sort of homebrew, as it could really mess up your Sony handheld if you're not careful. With that aside, enjoy!

- Source: QJ