Just go purchase a spare spring from the dealer for ~$3 and shorten. Here is a quote from a post I made in 2014...

"to lower the pressure you need to reduce the spring length. Reducing the spring length should have little affect on idle pressure, but will lower WOT pressure. I ended up taking 0.125" and that has given me 80psi at WOT, but still 20psi at idle."

I would start by shortening by ~0.080" using a sanding belt and then check pressure. Take off 0.020" chunks from there until you get the pressure you desire.

 

Wow, so really not much at all. I was snooping around down there thinking how the hell am I going to get that spring out. Thin walled socket, and move the oil cooler lines?

 

I was able to put a socket on it and remove without touching anything else, but it was a tight fit. When you purchase the new spring also purchase a new copper crush washer for the spring cover.

 

I wanted to bring the oil pressure down a little so I had the oil relief ported slightly. This brought pressure from 120+ at high rpm to 95-100psi measured at the oil filter housing.
This fits the 10 psi per 1000 rpm rule well.

5-40 oil, 8200 rev limit, 10K on a new engine/pump with stock oil pump gear. 30psi hot idle at 1200-1250rpm. It didn't change hot idle but cold idle went down from 90ish to 75-80ish.

Doing this mod or changing the spring will also lower pressure to the HLA and turbo feed line. I also have before and after data for the turbo feed line.

If someone is going to port the relief start small and work from there. Smooth is going to be more important then large.