There’s no reason why this wouldn’t work as long as you are good with the higher TSS. I’ve used the Sustained Power Build a few times in the build up to races rather than the triathlon plans.
There are many ways you can modify the plans - the way you suggest would be fine I’d imagine - if you are dropping one ride I’d think about dropping the Monday ride with shorter intervals for the long ride but if you feel you’d get value from the shorter stuff drop one of the others.
Dependent on your IM experience I’d also ask whether you feel you need the longer rides at all at the moment. May is a long way away yet and you may benefit from following the plan as prescribed and introducing longer rides in the couple of months preceding your race. It just depends on what type of riding feel you’d benefit from the most.