SEO newbie here. I'm working on a site redesign for a plumbing company. They want to switch their target audience from residential customers to commercial. The current site contains a lot of unique content about residential plumbing and their page rank is good. So I'm worried that when I relaunch the site without all that "residential" content, their page rank will suffer.
If I retain all the "residential" content and use 301s to redirect to it, or just keep the URLs the same - but don't include any internal links to that content (making it invisible to users of the new site) - will that work to retain the rank they've earned from the old content? Any suggestions for a better strategy? Thanks!