I've tried to quit many times but always failed. Perhaps is it a better goal to just try to moderate it?
What
@mime already said... if it's being a negative trait to you, moderate, or try some help from psychologist (always the better choice).
What methods or types of thoughts do you practice to moderate the amount of time you spend on porn/visual novels/games?
Main method: do something else to fill the time spent watching porn.
With this in mind, you decide what that something else will be.
In my case, I spend energy doing some sports, hiking to waterfalls or going to the beach, and having dates/sex IRL.
Why did I mention something physical? Because that's usually what releases endorphins! But you can find other things that generate a feeling of satisfaction, of fulfillment.
Pornography is associated with addiction due to the endorphin (raising serotonin/dopamine) generated in the moment. It's an addiction because you start to feel that what you already consume is not enough and you look for other alternatives, other games, other themes.
Do you plan on ever quitting entirely?
Probaly not. I used to be addicted.
Today I consider it a hobby. I can go without it, regardless of the time, without suffering because of it.