Is it permissible to disseminate and say: "O reassured soul, return to your Lord, well-pleased and pleasing [to Him], and enter among My [righteous] servants and enter My Paradise" upon hearing news of a death, knowing that some consider this to be a judgment that the deceased is destined for Paradise?

Writing or mentioning a verse (from the Qur'an) upon hearing of a Muslim's death does not necessitate a definitive judgment about their fate as being among the people of Paradise. This may rather be an act of optimism for them, hoping for a good destiny and mercy. The Sunnah (definition) (prophetic tradition) upon affliction is to say: "Indeed we belong to Allah, and indeed to Him we will return."