Yes, you can usually install a memorial plaque on a park bench, but whether it affects the warranty depends on how the plaque is attached and what the manufacturer allows. Most park bench warranties cover defects in materials and workmanship, not changes made after purchase. Drilling into the frame or wooden slats is the biggest concern because it can void coverage for rust, rot, or structural failure in the drilled areas.
Before you do anything, check the warranty documents or contact the bench manufacturer. Some companies will approve a small plaque if you use predrilled holes, stainless steel screws, or an adhesive mounting system that does not penetrate the protective coating. Others may ask you to place the plaque on a backrest slat that is easy to replace. If the bench is located in a public park, cemetery, or HOA common area, you also need permission from the organization that owns the bench.
If you want to protect the warranty, choose a mounting method that minimizes damage. Adhesive-backed bronze or aluminum plaques are often safer than screws because they do not create holes where water can enter. If screws are required, use marine-grade stainless steel and seal the holes with a non-corrosive sealant. Ask the manufacturer if they can pre-drill or recommend an installer, because a manufacturer-approved method is more likely to keep the warranty intact.
Keep a record of any written approval from the manufacturer or park owner. That way, if you need to make a warranty claim later, you can show that the plaque installation was approved. If the manufacturer says the warranty will be partially voided, ask which parts remain covered. In many cases, only the specific modified areas are excluded, not the entire bench.
In short, yes, you can install a memorial plaque on a park bench, and with a little planning you can often do it without losing the warranty. The key is to avoid unnecessary holes, use weather-resistant materials, and get approval in writing before you mount the plaque.