I am assuming you want to make the FST 90 play stiffer? If that is what you’re asking, there is 10 inches of parallel tip length. The R flex trim instructions calls for our IR3 trim instruction, which starts at 2″ on a #3 iron and goes to 5.5″ on the Wedge. You could trim an additional inch, starting at 3″ tip trim on the #3 and progressing 1/2″ increments to the wedge and trim 6.5″. There is enough parallel tip trim to do so. That would probably get you to a soft S or a firm R, however you want to look at it. At a 41″ raw length, you would need to be aware of the effect the additional tip trim will on the overall playing length. If you are installing in irons with traditional hosel bottom of the bore to ground dimensions (generally 1″ on irons), you should be able to make a standard length set.