Is it permissible to add words

Q 1: is it permissible to greet a fellow Muslim saying: "Al-Salamu `Alaikum wa Rahmatullahi wa Barakatuh wa Maghfiratuh (Peace, Mercy, Blessings and Forgiveness of Allah be upon you)"?

A: It is related by Abu Dawud and Al-Tirmidhy, who graded it as Hadith Hasan (good Hadith), on the authority of `Imran (may Allah be pleased with him) that he narrated, A man came to the Prophet (peace be upon him) and greeted him saying, "Al-Salamu `Alaikum (peace be upon you)" and he replied to him. When the man sat down, the Prophet (peace be upon him) said, "Ten (good deeds)." Another man came and greeted him saying, "Al-Salamu `Alaikum wa Rahmatullahi", and the Prophet (Peace and Mercy be upon him) replied. When the man sat down, the Prophet (peace be upon him) said, "Twenty." A third man came and greeted him saying, "Al-Salamu `Alaikum wa Rahmatullahi wa Barakatuh (Peace, Mercy and Blessings of Allah be upon you)", and the Prophet replied. When the man sat down, the Prophet (peace be upon him) said, "Thirty." It is also related by Abu Dawud on the authority of Mu`adh ibn Anas (may Allah be pleased with him) who narrated that a man came and greeted the Prophet (peace be upon him) saying, "Al-Salamu `Alaikum wa Rahmatullahi wa Barakatuh wa Maghfiratuh". Then the Prophet (peace be upon him) said, "Forty (good deeds)," and he added, "Thus are the virtues." However, this narration containing the addition "wa Maghfiratuh" is weak and cannot stand as a proof. (Part No. 24; Page No. 117) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.