When you do the split do you have to alter the amount of hops you put in, or do you just stick to the recipe?!
If you want to brew the beer that the recipe designers intended, then you need to alter your hops and possibly your malts. That said, you will still get beer even if you don't, so it depends on what you mean by "have to".
I tend to balk when people suggest that late extract additions are "better". There are plenty of things that are just flat out better in brewing: using a sanitizer is always better than not using a sanitizer; pitching yeast at appropriate rates is always better than just chucking in whatever you have; fresh ingredients is better than stale ingredients. But this isn't like that
The article JonK cites suggests three advantages of late addition:
1) lighter color
2) more hop bitterness
3) less carmelization
That is all very true, but I could just as easily say that the advantages of early addition are:
1) darker color
2) less hop bitterness
3) more carmelization
Color, hops, and carmelization are not inherently good or bad things in brewing the way that, say, sanitation is. They are particular traits of a beer, and likewise they are more or less desirable depending on the style you are going for.
This point really comes home when you are following somebody else's recipe. If they do an early addition and you do a late addition, you will get a different beer than they intended. It might even be a beer you like better, but all that demonstrates is that you have different tastes than the recipe designers. When I cook Indian food, I tend to double the recipe's garlic and halve its ginger because I know that I like garlic more than most people and ginger less, but I wouldn't go onto a cooking website and tell everyone that halving ginger requirements is part of good cooking procedure.
I certainly don't mean to discourage experimentation; quite the opposite. Knowing what you like is the key to coming up with some great recipes. That said, think of early vs. late addition in the same way you would think of American malt vs. British malt. Understanding the difference between them can help you really dial in a recipe, but it doesn't make sense to just automatically replace all domestic 2-row with Marris Otter. Unless, of course, you determine that you just flat out prefer British malts to American.