How MTB Labs migrated an outdated theme with zero downtime and 40% faster performance
A fashion retailer was running an outdated version of the Impulse theme (2.4) that couldn't support modern features and was causing performance issues. They needed a full migration to the latest version without disrupting their business.
The Challenge
Legacy theme holding back the business
The store had been running Impulse 2.4 for years, accumulating custom code and workarounds. The outdated theme couldn't support new Shopify features, had poor Core Web Vitals scores affecting SEO, and made simple updates risky due to technical debt. Previous attempts to update the theme had broken functionality, making the team hesitant to touch it. But staying on the old version meant falling further behind competitors with faster, more modern storefronts.
The Solution
Audit & Documentation I catalogued all custom sections, snippets, and modifications in the existing theme. This included identifying which customizations needed preservation versus which could be replaced with native Impulse 8.1 features, ensuring no critical functionality would be lost.
Staged Migration Rather than attempting a risky direct switch, I built the new theme on a development store and migrated custom functionality piece by piece. Each component was tested thoroughly before any customer-facing changes were made. This methodical approach eliminated the risk of breaking the live store.
Performance Optimization I leveraged Impulse 8.1's improved architecture while adding additional performance enhancements. This included optimized image loading strategies, reduced JavaScript bundle sizes, and improved critical rendering path—addressing the Core Web Vitals issues that were hurting their search rankings.
Zero-Downtime Launch I coordinated the theme switch during a low-traffic window with instant rollback capability prepared. After launch, I monitored performance and functionality closely for 48 hours to catch any edge cases and ensure everything worked perfectly.