Final answer:
To prevent overwriting functionality after deploying an update to the account operation class, you would manage the auto-resolve feature's settings or metadata. However without context on the deployment tool being used, it's hard to give a specific answer based on the provided options. Generally exclusions are managed within the deployment tool's configuration.
Step-by-step explanation:
After deploying an update to the account operation class, the QA team noticed some previous functionality was overwritten by the Auto-Resolve Functionality. To prevent this issue for all new promotions, you should typically follow best practices in configuration and version control. For this specific scenario, this would entail managing the settings or metadata that govern the auto-resolve feature.
However since the options provided in the question ((a) Exclude Apex Classes in the Exclude From Autoresolve field in the Pipeline Record, (b) Exclude Apex Classes in the Exclude From Autoresolve field in each User Story Record, (c) Exclude Apex Classes in the Exclude From Autoresolve field in the Destination's Org Credential Record) appear to be referencing a specific deployment pipeline configuration, without information on the actual platform or tools being used (such as Salesforce, Jenkins, or another CI/CD tool), it's impossible to give a definitive answer. In general terms, you would want to exclude certain classes or objects from being auto-resolved during the merge of code in your environment settings. Typically such exclusions are managed within the deployment pipeline's configuration or within the specific settings for merging strategy for a given release.