Salam is a kind of Prayer, so there’s no harm if a Prayer is extended with relevant and appropriate words. Quran says:
وَإِذَا حُيِّيْتُم بِتَحِيَّةٍ فَحَيُّواْ بِأَحْسَنَ مِنْهَا أَوْ رُدُّوهَا إِنَّ اللّهَ كَانَ عَلَى كُلِّ شَيْءٍ حَسِيبًا اللّهُ لا إِلَـهَ إِلاَّ هُوَ لَيَجْمَعَنَّكُمْ إِلَى يَوْمِ الْقِيَامَةِ لاَ رَيْبَ فِيهِ وَمَنْ أَصْدَقُ مِنَ اللّهِ حَدِيثًا
[Go out for war] and if salam [is said by any person], you also reply by saying salam in a better way or in the same way [and do not oppress anyone] because God indeed will take account of everything. There is no god but God. He shall indeed take you all to the Day of Judgement in the advent of which there is no doubt. And who is more truthful than God? (Quran 4: 86-87)
(Excerpt from Quranic Exegesis: Javed Ahmed Ghamidi)
(Translated by Dr. Shehzad Saleem)