Short answer. Not automatically. Article 1746 of the Civil Code lets you have the waiver annulled if the courier, as a common carrier, refused to accept your package unless you signed away its liability. A waiver you were free to refuse stands on different footing than one presented as a condition of shipping at all.
What the law says
An agreement limiting the common carrier's liability may be annulled by the shipper or owner if the common carrier refused to carry the goods unless the former agreed to such stipulation.
Civil Code, Article 1746 — Coerced Limitation Annullable. Read the full provision →
The rule is about how the waiver came to be signed
Article 1746 does not ask whether a waiver exists on paper — it asks how it got there. It provides that an agreement limiting the common carrier's liability may be annulled by the shipper or owner if the common carrier refused to carry the goods unless the former agreed to such stipulation. If the courier's real position was "sign this or we will not take your package," the resulting waiver is exactly what this article lets you challenge.
Why couriers are held to this standard
A common carrier holds itself out to serve the public, and a shipper with an urgent package rarely has room to negotiate or walk away to a competitor on the spot. The law treats a waiver extracted under that kind of take-it-or-leave-it pressure as suspect, because the shipper's "agreement" was not a real choice — it was the price of getting the package accepted at all. Article 1746 exists precisely to keep that imbalance from being used to strip away liability that would otherwise apply.
What annulling the waiver actually does
Annulling the waiver under Article 1746 removes the limitation you were made to sign — it does not, by itself, prove that the courier lost or damaged your package, or fix an amount you are owed. Those remain separate questions to be established on their own facts. What the article gives you is the ability to argue that the stipulation limiting liability should not bind you in the first place, because of the circumstances under which you were made to accept it.
What strengthens a claim like this
Keep whatever shows the waiver was presented as a condition rather than a choice: the shipping form itself, any note that acceptance depended on the signature, staff instructions, or messages confirming the package would not be taken otherwise. The more clearly the record shows refusal-unless-signed, the stronger the basis for treating the waiver as annullable under this article rather than as a freely bargained term you are simply stuck with.