When introducing new configuration options or making changes that could be disruptive, make them opt-in by default rather than enabled automatically. This prevents breaking existing functionality and gives users control over when to adopt new behaviors. Key principles: - New features should be disabled by default with explicit flags to enable them - Potentially disruptive migrations should require explicit opt-in - Breaking configuration changes should be avoided, or made opt-in with clear migration paths - Validate configuration options and provide clear error messages for unsupported settings Example from migration configuration: ```typescript // Bad: Automatically migrating potentially disruptive changes export class NgClassMigration { // Always migrates multi-class keys, potentially creating verbose output } // Good: Making disruptive changes opt-in export class NgClassMigration { constructor(private options: { migrateMultiClassKeys?: boolean } = {}) {} migrate() { // By default don't migrate multi-class keys if (!this.options.migrateMultiClassKeys) { return; // Skip potentially disruptive migration } // Only migrate when explicitly requested } } ``` This approach protects users from unexpected changes while still providing access to new functionality when they're ready to adopt it.