It changes the script to have a 30-rd magazine, shoot at 600 rpm and do the same damage as the default Desert Eagle. As it's the rifle script not the desert rifle script, it loses the 3-rd burst feature, too. If you get the M16A2 script, you'll also have an M16-looking thing that *does* fire 3-rd bursts and is otherwise pretty much identical to this.
(The Hunting Rifle script that goes with these gives it the same 360 spare carried and the AK47 mod that goes with them gives it higher damage too, proportional to muzzle energy. It turns out that 7.62x39mm : 5.56x45mm muzzle energy is 105:80, not far off the 58:44 ratio of the default AK47 and default SCAR-L.)

Does this mod change the script of the SCAR to match a real-world counterpart or is it just a model swap? I have the same question for the M16A2 version.

Yes. That's what it is with or without this mod. This mod and the M16A2 mod mentioned in the description, put together, move the 3-round burst feature onto the correct model, but they're both automatic rifles.

I think that the Scar-L is automatic rifle

Ok so there is a change in the physics, guess I'll just have to try it out to see what I think.

Pretty much, but it's got real-world 30-rd magazine, not the default 60-rd mag, and it hits like a 5.56mm rifle: http://www.youtube.com/watch?feature=player_embedded&v=tku8YI68-JA#t=302s

So does this mod make the rifle act just like the (M-16/AR-15/M-4/whatever) assault rifle but look like a SCAR-L?