def SetMemberComment(sid, member_offset, comment, repeatable):
    s = idaapi.get_struc(sid)
    if not s:
        return 0

    m = idaapi.get_member(s, member_offset)
    if not m:
        return 0

    return idaapi.set_member_cmt(m, comment, repeatable)
Change structure member comment
dataset/ETHPy150Open EiNSTeiN-/idapython/python/idc.py/SetMemberComment