Immersion guide
Take a look at that guide it might have what you are looking for.
Anything specific you are looking for that addon to do that others cant?
Does the addon still work?
If so and the only problem is that it's marked as out of date then you probably just need to change the version number, which can be done via Windows Notepad. But in that case you could also just check the box on the addon menu to enable out of date addons, which will allow it to run even if it shows as being out of date.
If it's not working then things get more complicated because it depends on what the problem is. It might be a quick fix, or it might require an extensive re-write of the code which only an experienced addon author could do.
There's a Wiki on ESOUI.com which explains how to create addons, which can be used to learn how to edit them as well. (A while ago I taught myself to make account-wide addons character specific via that site.) But some changes are easier to make than others, so it really depends on what exactly needs to be done.
Immersion guide
Take a look at that guide it might have what you are looking for.
Anything specific you are looking for that addon to do that others cant?
Yeah, the addon I mentioned makes your attribute bars invisible and when you lose health, you get flashing red filters on the side of the screens. Which makes the player not look at the bottom of the screen during combat, but and the enemy.