It seems you're trying to nuance the passages. Wouldn't God's foreknowledge of who will believe therefore make the prayers particular for those who specifically believe?Actually no I would have to disagree. Note the words "I pray also for those who will believe in me through their message" to me that indicates He prays for those unbelievers who will in the future come to Him, those that did believe the gospel message. Since most people that would trust in Christ had not been born yet they could not be considered believers in Christ could they. No one is born as a believer are they? But when they trust in Christ they receive the gift of eternal life.
I agree with Heb 7:24-25 but those verses do not say He only prays for believers. What it does say is that He intercedes for those that believe, those who draw near to God through Him. When Satan accuses believers Christ stands as our advocate and pleads our case.as it were.
If God has no idea who was going to be saved, I could follow your thoughts here, but since God does know, the prayers are particular to those who will believe, regardless of whether they have believed at the time of the prayer.