I am extending my office lease and the Land Lord has added this to the amendment
Real Estate Attorney
A Civil Code section 1542 waiver releases all claims that you may have whether you know about them or not. If you think you may have claims against the Landlord arising out of your tenancy, you should discuss them with an attorney before signing the lease extension.
This answer does not constitue legal advice, nor does it creat an attorney/client relationship. If you are seeking legal advice upon which you intend to rely, you should hire competent cousel familiar with this area of the law in your locale.
By waiving Civil Code 1542, you would be releasing all claims against your landlord, whether actual or potential, known or unknown. In the case of residential leases, some claims cannot be waived, e.g., claims based on warranty of habitability, right to quiet use and enjoyment, etc. But in the case of a commercial lease like yours, where the parties are deemed to possess a certain minimum level of business sophistication, almost anything goes. And it usually goes in favor of the commercial landlord. I would look long and hard at the renewed lease -- and the premises -- before signing away all known and unknown claims in my favor. Better still, you should have a qualified attorney review the lease renewal before you sign it.