How to best solve IM change-retention change lag

Let’s say I’ve been using a deck for 3 months at 85% retention. In 1 week, I will take the exam that the deck was made for. I want to get a 95% on the test so I bump up my interval modifier to change my retention to 95%. The problem is that the current intervals of the cards are long since I’ve been using the deck for a while (3 months). It’s likely that most of the cards have current intervals that will end after the test takes place, which means I won’t have 95% retention for most of the material at the time of the test. I was thinking I could cap the maximum interval so that it’s guaranteed I have 95% retention for all the material but I’m worried this would stunt the growth of many cards. What is the best way to handle the lag in change in IM and change in retention.