To determine the correctness of the given statements about chemical reactions, let's analyze each statement:

1. Statement I: "Every reaction in which two or more reactants combine to form a single product is classified as a combination reaction regardless of heat change."
   • A combination reaction is a chemical process where two or more reactants combine to form a single product. For example, when hydrogen gas reacts with oxygen gas to form water, it is a combination reaction: 2H_{2}(g) + O_{2}(g) \rightarrow 2H_{2}O(l).
   • The definition of a combination reaction does not inherently depend on the heat change (e.g., exothermic or endothermic nature). It is solely described by the formation of a single product from multiple reactants.
   • Therefore, Statement I is correct as it accurately describes the essence of combination reactions without limiting them to any heat exchange conditions.
2. Statement II: "The reaction CaO(s) + H₂O(l) → Ca(OH)₂ (aq) + heat is both a combination reaction and an exothermic reaction."
   • The chemical equation provided describes calcium oxide reacting with water to form calcium hydroxide. This is indeed a combination reaction as it involves two reactants combining to form a single product.
   • This reaction is also exothermic because it releases heat, signifying that the system releases energy to the surroundings when CaO reacts with H₂O to form Ca(OH)₂.
   • As both descriptions match the characteristics of a combination and exothermic reaction, Statement II is correct.

After analyzing each statement independently, we can conclude:

• Both Statement I and Statement II accurately represent facts about chemical reaction types and characteristics.

Correct Option: Both statements are correct.