Does a board have to switch carriers to become warrantable again?
Usually not. Most warrantability problems are fixed by adjusting the existing master policy: lowering the deductible with a buyback, moving from actual cash value to replacement cost, adding ordinance-or-law, or correcting fidelity limits. The goal is to optimize the policy you have, not to trigger a disruptive carrier change, though a re-marketing can help if the current market is unwilling.