定语从句先行词地方

托福TPO16的一个句子 In 1990, new rules and guidelines were adopted in the United Kingdom that has changed the whole field of Archaeology in that country。后面的that has changed the whole field of Archaeology in that country是定语从句吗？先行词是不是“new rules and guidelines”。定语从句和先行词可以分得这么开吗？

that为主语，has changed谓语为单数，比较容易排除复数先行词的。