Does not Qadi Iyad's statement in his commentary on the Hadith: "You will indeed follow the ways of..." mean that the prohibition of imitating disbelievers is restricted to what is Islamically unlawful for us, and should we therefore not use this Hadith to prohibit celebrations such as Mother's Day and birthdays based on this understanding?

It is not permissible to imitate non-Muslims in matters that are religiously forbidden or blameworthy, even if their origin was permissible. The Prophet (peace and blessings be upon him) encouraged differing from them in many matters, and warnings against imitating previous nations in their actions and morals have been narrated from the Companions, the Tabi'un, and the scholars of the Ummah. Commentators have mentioned that the hadith is not limited to forbidden matters but also includes innovations (bid'ah) and misguided desires, and that imitating Jews, Christians, Persians, and Romans is blameworthy.