I'd dedicate 1 headstamp to converted/reformed brass, and sharpie mark them.
I did think about resizing 308 to 7-08, but decided while I could reform/resize, i would get once fired cases instead.
Now a 7 valkrie that looks obviously diffrent, is a non issue for me. But no choice there in headstamped brass, it has to be formed from other cases.

I also saw where someone scored a line on the base of the case through the original headstamp.