If you have all the equipment to monitor your afr, I don't see any reason why you can't use a fcd.
I use one in my vehicle due to my upgrades flowing that much more air that before fcon with my ecu it managed to throw cut in heh.
Just bear in mind that by using the fcd, it won't remove it, it just scales it up further, you can use a fcd and pray that your mods don't go as flowy as mine. Ideally you will need to obtain an aftermarket ecu for the end game.
Atm, with hks fcon, rx7 550 inj, custom intercooler/piping, to4b h trim garrett, 3" exhaust I was pushing 340hp at the wheels on 14.7psi with really really really bad fuel tuning (no fuel cut either), it was tanking in the 9's for afr wot so I now just patter it around town daily driving it till I can give it the ecu it deserves
TBH if you're hitting cut at 9psi, you more than likely have a leak somewhere, double check the basics first as you don't wanna miss something little and have it damage your car. On the other hand, before the fcon I was also hitting cut, but yeah just make sure you've covered the basics.
What is your afr at idle?
The other thing to remember folks that may read this in future, 7mgte fuel cut is very abrupt/violent, it will rev out and then it will be like someone just killed your ignition, it will take a few secs to come off fuel cut, then when boost gets back up to max it will do it again, it's like hitting a brick wall. Make sure you are indeed hitting fuel cut and not experiencing another ignition problem, also the check engine light should illuminate when hitting cut but it can also illuminate when having other problems
Do yourselves a favour and check your codes, fuel cut should throw a 34 iirc, abnormal turbocharger pressure.... amusingly enough
Other regulars feel free to correct or add information, it's been a while since I had a stockish car with stockish problems
GL