When did the changes made by this act take effect?
From the given context, it is not explicitly mentioned when the changes made by these acts took effect. However, specific dates are provided for some of the amendments, such as:

1. Subs. by the Constitution (Fifty-first Amendment) Act, 1984, s. 2, for sub-clause (b) (w.e.f. 16-6-1986).
2. Ins. by the Constitution (Seventh Amendment) Act, 1956, s. 29 and Sch. (w.e.f. 1-11-1956).
3. Ins. by the Constitution (Thirty-first Amendment) Act, 1973, s. 3 (w.e.f. 17-10-1973).
4. Ins. by the Constitution (Forty-second Amendment) Act, 1976, s. 47 (w.e.f. 3-1-1977).
5. Subs. by the Constitution (Eighty-fourth Amendment) Act, 2001, s. 6, for "2000" (w.e.f. 21-2-2002).
6. Subs. by the Constitution (Eighty-seventh Amendment) Act, 2003, s. 5, for "1991" (w.e.f. 22-6-2003).