I am not sure why you included my quote in your reply. Sure, if you want to change your mast rake you must change your forestay length. But the forestay tension in a mast head rig will be determined by your back stay tension. And if you back stay is longer than your forestay (generally the case), then your forestay will always be at a higher tension than the backstay- in my case 1.25 x the backstay tension.
I quoted your post because you were responding to ron hudson who was questioning how he could measure the tension on his furlered Forestay. IMO the simple answer is: You can't. Also confirmed here:
How to use 90 & 91 Series Tension Gauges
I don't think the Forestay tension should matter as long as :
You have proper mast rake, correct forestay sag, and don't exceed the maximum tension limit of your backstay. I don't understand what the 1.25 number does for you.