Tested on the i9500 5.01 TW leak.
In the generic.kl file, key 217 is the hold left button. On the S5 this is actually set to MENU so the function is still there.
Key 254 appears to be hold home but as someone already mentioned, modding another file is needed to change that.
I set 217 to MENU and it works fine, set 254 to SEARCH but it still stays as APP_SWITCH.
Tested changing the home and right and was able to change their function.
So to summarise -
LEFT = 139
HOLD LEFT = 217
HOME = 172
HOLD HOME = 254 (changing has no effect)
RIGHT = 158
HOLD RIGHT = ?