Generally, a new law in Kuwait applies from the date it comes into force and does not retroactively alter contracts you have already signed. Under Article 3 of the Kuwait Civil Code, the effects of legal transactions (including contracts) remain governed by the law that was in force when those transactions were concluded.
However, there is an important exception: if the new law relates to public policy (النظام العام), it can apply immediately to existing contracts and ongoing obligations. Public policy provisions are those the Kuwaiti legislature considers fundamental to society and the legal order — such as rules about usury, certain employment protections, or mandatory licensing requirements. This means a new public-policy law could override specific contractual terms even in agreements you have already entered into.
As a practical step, whenever a new law is announced that is relevant to your business or tenancy arrangements in Kuwait, check with a local lawyer whether it carries a public policy designation. If it does, you may need to amend existing contracts to remain compliant.
This is general legal information, not legal advice. For advice on your specific situation, consult a lawyer licensed in Kuwait.