Why can't you change the Shift+Space combination to some unlikely combination
like Alt+F12 or whatever ?
This is not the same as totally disabling it, but it will liberate at least the space-bar.

As more experimentation, I believe that this key-combination is defined in the registry at :
HKEY_CURRENT_USER\Control Panel\Input Method\Hot Keys\00000011.

Export this registry-key to a .reg file and change the following items :
Key Modifiers to "00 C0 00 00", meaning no "Control" or "Shift" or "Alt".
Virtual Key to 0, meaning "None".

If this does not work, maybe a more forceful action is required, such as totally deleting the 00000011 key. Unfortunately also, this thread claims that Windows will reset these keys
as soon as they are changed, which you can verify on your computer,

(The above is based on Simplified Chinese MSPY 3.0 IME Hot Key Registry Settings.)

A reboot is required to be absolutely sure that any such change had an effect.
Create also, as a safety measure, a system quite-point before modifying the registry.

[EDIT]

It seems like Windows will not suffer a change to the above registry keys, so any changes
are immediately nullified.

The only working solution is to use AutoHotkey to replace the Shift+Space combination to something else.

One possibility is detailed here : "+Space::Space".
The poster actually used "+Space:: WinActivate".

How to disable the shape toggle hotkey in Windows Chinese Input method?
There are three Kamui in the show: Senketsu, Junketsu and Shinra-Kōketsu (Omnisilk Kōketsu). 



Shinra-Kōketsu is on another level in comparison to other Kamui, but Junketsu is the same with Senketsu, but he never talk. Is Senketsu different from other Kamui?
