Uniform Civil Code means 'Common Set of Laws of All People'. india is a union of states, each state has its own separate law, and each state can interpret it as per its own. Since it comes in the state list, every state has the right to make a law.
The supreme court has given that you can live in a live-in relationship but it is the job of the state how it implements it. The government of uttarakhand has not said that you cannot live-in, or cannot live together, but has simply imposed a clause that you will have to report. This comes under the purview of the state government.
The state government is free to impose any term or condition. All the issues of law and order come under the jurisdiction of the state, hence it is not illegal but legal. The law that is made becomes law only when the court gives its permission. Whatever the law, there will be opposition to it, some people will be in favor and some will be against it. There will be complaints of someone saying why STs were left out, why we were not kept. Scheduled Castes have been given some exemption under Article 21 of the Constitution. It should be studied in detail.
Uniform civil code necessary
There are different rules and regulations for all religions, and all the religious communities in india are based on personal law. These have been codified over time, like for Hindus there is Hindu marriage Act, Hindu Succession Act, for Christians there is Christian marriage Act, for Parsis there is marriage and Divorce Act, indian Divorce Act, but Muslim personal law is not codified, that is based on their religion. Theirs is according to Shariat.