Of course a thorough drain and flush is best, but even a partial drain and refill replenishes the additives and is better than nothing.

I like to use distilled water from the grocery store; the empties are handy for old coolant, among other things.

Owners Manual only recommends 60/40 mix for the coldest climates but I don’t see the problem with doing it everywhere.

On one car (not HHR) I used a Prestone flush kit with a fitting you insert in a heater hose for connection to a garden hose. Was pretty handy except the cap wouldn’t stay tight and it took awhile to figure out where the coolant was being lost.