How to remap 'Shift & Up/Down arrow keys' to type actual up & down arrows?
KeyRemap4MacBook currently can't insert arbitrary text. For something like this, I'd recommend using DefaultKeyBinding.dict.

Create ~/Library/KeyBindings/DefaultKeyBinding.dict and enter

{ "$\Uf700" = (insertText:, "↑"); "$\Uf701" = (insertText:, "↓"); }


$ = shift, \Uf700 = up, \Uf701 = down, insertText: will insert a string at the current cursor location

Quit and reopen applications for the change to take effect