Can you elaborate on why you are thinking you have to change brake lines just as a result of a frozen caliper? I've NEVER changed brake lines for anything other than an upgrade to stainless steel lines to allow for a firmer pedal by taking the expansion of the rubber lines when under pressure out of the mix of possibilities. You should just be able to swap out (or 'rebuild' your calipers), bleed out the old fluid, and be good to go. Just remember to replace your calipers in pairs - uneven braking is all bad.