Take a 700F tip and pull out the curie point metal back and replace with a 600F one from another tip. That does work well, I did it when I got a lot of 800F tips from the stores as that is what they had, and I was not wanting to cook the fragile PCB's I was working on. When I bought a flat pack bit ( I wanted one so paid for it myself, less hassle) it came as the model without a curie point back, so simply added one into the existing hole there, as Weller made it for ease of bit use on the new stations. Just had to be careful in screwing it into the head that the metal block did not skew and that it did come out with the tip.