--newer engine mods automatically raise the idle when anti-ice and ignition switches are on, in addition to the redesign of the
My understanding is that the minimum of 45%N1 was the quick fix until the modification to flight idle came into vogue. This ensured ground idle was around 22% N1 and in flight idle became around 32% N1. Once the new flight idle was introduced, the automatic increase in N1 associated with the start switches or engine anti-icing switches on, was no longer needed. Nor was 45% N1.
I assume therefore that the current reference to minimum N1 in moderate to heavy rain etc is the manufacturer covering the case where the old 45% N1 advice is still valid. But I cannot be certain of that - hence the initial query.