Is the regular recitation of Surahs Al-Mulk and Al-Kahf during the Night Vigil Prayer, each Surah at its prescribed time, considered an innovation (bid'ah) or a permissible and recommended act?

Reciting Surat Al-Mulk is a means of salvation from the torment of the grave. The Sunnah is to consistently recite it every night before sleeping. It is also recommended to recite Surat Al-Kahf on the night of Friday or during its day. There is no evidence confirming the specific recitation of these two surahs during Qiyam al-Layl (night vigil prayer), but there is no harm in doing so if one does not intend to specify this particular time. However, consistently reciting them at this specific time and believing that it is a Sunnah would be considered an additional innovation (bid'ah idafiyah).