Model (USA) Rule of Evidence 407: Subsequent remedial measures are not admissible as evidence to prove negligence, culpable conduct, a defect in a product or its design, or a need for a warning or instruction.
But the court may admit this evidence for another purpose, such as impeachment or — if disputed — proving ownership, control, or the feasibility of precautionary measures
EDIT: I’m not looking up the contextualing comments that accompany the rule, but I will share what I remember from law school many years ago: this rule exists for public safety. You don’t want to penalize fixing a dangerous situation, regardless of the facts of any specific case.