This is currently not easily done.
I just checked, and the shortcut is hard-coded into the plugin :?. That means the only way to change it is to compile from source after editing the line that says
m_EditMenu->Append(idMenuCodeComplete, _("Complete code\tCtrl-Space"));
in
codeblocks/src/plugins/codecompletion/codecompletion.cpp (it's in
CodeCompletion::BuildMenu) to use your new shortcut setting, in your case changing it to
m_EditMenu->Append(idMenuCodeComplete, _("Complete code\tF12"));
should work.
It might have been easier if the codecompletion plugin loaded its menu from an resource file, then you'd just have to edit a .xrc file in
${CODEBLOCKS_DIR}/share/CodeBlocks/codecompletion.zip, which could be done without getting the source and compiling.
IIRC keyboard shortcut editing is planned to be added, but only after version 1.0 is done.
But until someone changes the codecompletion plugin to load the menu from a resource file (Devs: this is a hint
) or the keyboard shortcut settings are implemented post-1.0, the above is the only way to do it, I'm afraid.