Google clarifies its position on partial site migrations, a practice that may seem appealing but can have disastrous consequences. The address change tool in Search Console is designed for a specific scenario: the complete transfer of a site from domain A to domain B.

The case mentioned illustrates an atypical migration: moving only the homepage to a new domain while keeping product and category pages on the old domain. This hybrid architecture poses a fundamental problem for Google's algorithms.

Google expects a binary migration, a clear-cut switch between two states. Migration processing systems are not designed to understand a modular distribution of content across multiple domains. This approach would create confusion in indexing and the transmission of SEO signals.

• The address change tool only works for complete site migrations
• Partial migrations are not recognized as genuine site changes by Google
• A split architecture between two domains disrupts algorithmic understanding of the site
• 301 redirects must cover the entire site for optimal PageRank transmission
• Maintaining traffic on a few old URLs is tolerated, but a dual architecture is not

This clarification from Mueller is perfectly consistent with what we've observed for years regarding successful migrations versus those that fail. Cases of partial migrations I've audited consistently show visibility loss, authority dilution, and contradictory signals sent to Google.

The important nuance concerns progressive migrations by sections. There's a difference between progressively migrating entire sections (the blog today, products tomorrow) with clean 301 redirects, and deliberately maintaining a fragmented architecture across two domains. The first approach can work if it's temporary and well-managed.

The common mistake is to underestimate the technical complexity of migrations. Many think they can optimize their strategy by keeping "the best of both worlds," but Google favors architectural clarity. One site, one domain, one coherent structure.

• Always plan a complete migration: if you're changing domains, plan to migrate the entire site, not just certain sections
• Use the address change tool only for total migrations: wait until 95-100% of content is migrated before activating this tool
• Implement comprehensive 301 redirects: every URL from the old site must point to its counterpart on the new domain
• Avoid permanent hybrid architectures: don't deliberately maintain important content on the old domain after migration
• If migration must be progressive, proceed by complete functional blocks (e.g., entire blog, then entire shop) with a tight timeline
• Document your migration plan before starting: identify all URLs, all content types, and establish complete mapping
• Monitor key post-migration metrics: organic traffic, indexing, crawl budget, rankings on strategic queries
• Maintain 301 redirects for at least 12 months: Google needs time to consolidate all signals on the new domain