re-torque head bolts first but how?

hi everyone.
today is supposed to be the big day when i remove the head (we'll see...).
anyways, as most of you know there is a bulletin from bmw that says something along the lines of "our engine block [may] become weak if it ever overheats, you will go through the trouble of getting the head machined, new head gasket, new head bolts and as you start tightening it down you realize the threads are pulling right out of the block.... so, before taking off the head it will be very wise to retorque the (old) bolts and make sure the block is "ok" and the bolts are able to torque down".

i did a lot of research, there is a ton of confusing information, and i have many questions. please correct me if i'm wrong!

first and foremost, the tightening procedure for the NEW headbolts is:
note: a special bolt pattern applies to each step (not covered here)
1: 30 footpounds
2: wait 20 minutes for good measure
3: add 90 degrees
4: wait 20 minutes for good measure
5: add another 90 degrees

during this procedure the NEW bolt will actually stretch slightly, i assume the stretching actually strengthens the bolt and prevents it from stretching further when you're driving around again.

i believe that the old bolts will not stretch so very importantly you can't follow this procedure on a bolt that was already used. if you do, it will or may pull out the threads even if your block was perfectly ok prior.

so on the one hand you're supposed to re-torque the old (?) bolts to see if the block can hold them, but it doesn't tell you how to do that for the re-torque scenario. should you loosen them first or can you check first if they were even still tight? what torque do you use, 30 footpounds?

re-torque head bolts first but how?