I think you are looking into the conditionals too deeply and reading too much into it.
The original sentence could be parsed as:
Obama also stressed that more sanctions were being prepared against Russia [to be put into action] if the West decided it ( Russia) engaged in activities which were destabilising to Ukraine.
Your rewrite changes the meaning considerably. The simple statement is that sanctions are being prepared - and the reason that they are being prepared is that maybe the West will decide in the future that Russia engages in destabilising actions.
Strictly speaking this use of if is a bit colloquial, I guess. It would be similar to
I made sure I prepared some extra sandwiches if I would feel hungry later on.
Basically, there is an elided for:
I made sure I prepared some extra sandwiches [for] if I would feel hungry later on.
If new sanctions were going to be imposed on Russia in future, it would be because of further possible destabilising activities in Ukraine.
Makes the sanctions hypothetical - which is strictly speaking correct, as they are only being prepared now - but that confuses the matter slightly.
The sanctions are being prepared. No hypothetical there.
The preparation is done with a purpose.
That purpose regards Russia's potential future actions.
If Russia's actions are seen as destabilising, the preparations will serve their purpose (that is, sanctions will be imposed).
Now, nowhere in the original sentence is there any implication that imposing the sanctions has to be only caused by those destabilising actions. There could be other reasons. But the purpose of the preparations is to be ready for those destabilising actions.