Change what backs the loan. Keep the loan.

The new collateral is supplied before the old is withdrawn. That ordering is the entire point: the obvious implementation withdraws first, and for the few seconds in between, the position is under-collateralised and a liquidator is watching.

Because it is one atomic transaction, a liquidator cannot act between the steps at all. And the contract enforces a minimum health factor after the swap — if the new collateral would leave the position weaker than you specified, the whole thing reverts and nothing has moved except gas.

Free. The receiver contract charges nothing for this. You pay the flash premium, the swap, and gas.

• Rotating out of an asset you no longer want to hold without giving up the borrow.
• Moving to collateral with a better loan-to-value, freeing borrowing capacity.
• Getting out of a collateral asset that is being delisted or having its parameters cut, which usually happens with notice and is a slow-motion liquidation if ignored.