NOOOOO. CYA is conditioner/stabilizer. You already have too much in your pool at 90. If you have passed your SLAM (meaning your water is clear also, right?) you just stop adding any chlorine in any form and let the FC level drift down "naturally". Just test once a day until it is back in the target range for your CYA of 90. Then, the TFP method is to add liquid chlorine once a day to keep your FC in your target range. Using liquid chlorine will not raise that CYA level any more.
If you want to do a water exchange to get the CYA down, you can do that, but if your water is clear and the FC holding overnight, you don't really NEED to. The daily dose of chlorine needed each day is the same whether you're at 90 or 40, so it won't save you any money. Having a lower target FC level will save you on testing chemicals though, as even at the 10 mL test it takes a lot of drops to test your FC.
edit: 7 is the minimum FC for a CYA of 90. You should start the day at 10 so it has room to drop through the day. Then test at night and bring back up (using poolmath to calculate the dosage required). After a week or so you'll get an idea how much FC you lose each day. Maybe you only need to be at 9 to start the day in the winter, as the FC burns off much slower. You'll have to know your pool.