Fuel Injector Opening Pressure

Hello fellow diesel enthusiasts,

I'm probably going to talk about a rather unusual topic now.
Here's the translation:

"This is about a Perkins diesel engine, likely from the 1960s."
It's a 4-cylinder, direct injection engine, without a turbocharger. It has a displacement of 4.4 liters.

My acquaintance and I are using it to power a generator in an isolated mode. Since this engine is somewhat oversized for the power output we're using (approximately 5-15 kW), it usually runs at a low load level, around 1200 RPM. Now, we want to "optimize" the fuel consumption, which means the fuel injectors need to be replaced. Given its age, it's probably not a luxury anymore.

Using a nozzle testing device, I discovered that several nozzles are worn out.
Den Öffungsdruck kann man bequem mit einer Schraube einstellen. Great! / Awesome! / Fantastic!
The pressure is specified as 170 bar at the factory.
Now, I've been giving some thought to the operation at partial load.
What would happen if the opening pressure of the new nozzles were slightly increased?
I'm thinking around 10-20%. Would that negatively affect combustion in the partial load range? Would it affect the starting behavior?
Of course, we are also considering adjusting the timing of the funding.