I can confirm that this method works. I recently changed the numbers mentioned and the update triggered right after the phone restarted.

However. I used a different method, with the same goal.
Since my market didn't work well, I couldn't download root explorer. so I used debugging mode, fetched the file in question, edited it and put it back again via the adb command.
Here's how I did it without Root explorer:

Activate debugging mode, connect the phone, but do not mount the sdcard (we need it in the device)
I assume you know the methods for this.
If not, the "search" button on these forums is your best friend. If you still have trouble with that, you shouldn't be reading any further.

DO NOT EXECUTE THE COMMANDS UNLESS YOU KNOW THE NATURE OF THEM!
I hereby disclaim all responsibility if you choose to execute the commands below.

Here's the commands once connected and debugging activated:
Code:

adb pull /system/default.prop default.prop

a new file with the name "default.prop" should appear in the folder where your command line where executed.
Edit it according to instructions posted by the Original Poster (OP) and save it.
it's preferred to use a real text-editor, such as notepad++ for this and not Windows own notepad.exe , as notepad.exe are known to "destroy" Unix type text files.

Once that's done here's how to put it back again and reboot the device:
Code:

adb push default.prop /sdcard/default.prop
adb shell mount -o remount,rw -t yaffs2 /dev/block/mtdblock2 /system
adb shell dd if=/sdcard/default.prop of=/system/default.prop
reboot

Once the phone boots up and if you've edited and saved the file properly, it should update once you mount it to the computer.