Read somewhere that I should not put Porterfield pads on new rotors. However I need to replace my warped rotors and would like to do it all at once. Is this a bunch of baloney, or is there something behind it?

New rotors are not heat cycled like used ones. If your rotors are 1mm near the stock thickness then go ahead and re-cut and use them. 1mm will not make that much difference on rotor temp.

Also consult the company you are buying the pads from about how you break them in. I usually drive around 50 miles of stop and go traffic then one run up the mountain to break them in.
no hard braking until the pads are well seated.

You'll be fine. Just follow the bedding in procedure recommended by the pad manufacturer, and you're all set

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo