Why until now you still believe Indian has leverage on Russian political decision. Let me ask you a basic fact, How did JF-17 got the RD-93 engine from Russian in the first place? China has a bigger political influence on Russian than Indian. It is solely on China account that Russian agree to sell RD-93 engine for JF-17. Even Singh who attempt to lobby for blocking of the RD-93 engine got bluntly rejected by Putin when he personally visited Russia in the 2008.So you are saying that Russians wont raise an issue if J-31 powered by RD-93 is sold to Pakistan? Moreover I have even read that the reason why PAF has delayed the purchase of J-10B is because Russian don't want their engines in Pakistan's hands, may be due to Indian pressure.
As for J-31, RD-93 can never satisfy J-31 engine. RD-93 is used just solely to speed up the development process. It will need the Chinese engine when the export model is finalised. And I do not understand why Pakistanis rather believe in western sources who dont even know a single Chinese for information regarding Chinese military development?