Restart campaign with new dlc?

[Schwarzburg]

I don't think I have ever installed a dlc.
Would you need to start a new campaign for a dlc to add new research, buildings, units and such?
Say I install the game, start a campaign. A week later I install the greek city states DLC which adds new mercenaries in the Hellas region.
Would I be able to recruit them in my existing campaign?
How was that handled in previous games?

I know changing something as unit size required a new campaign to take effect.

Maybe this is a stupid thing to ask, but it's late. That's my excuse and I'm sticking with it.

[GussieFinkNottle]

Maybe, maybe not. It's variable between different games (though quite likely).
You will have to play Rome 2 to see

[von stoker]

the greek city states (for example) are already in the game and controlled by the AI. it just means that they will become playable for you the next time you go to the start new campaign screen

[CDR Hurricane]

the greek city states (for example) are already in the game and controlled by the AI. it just means that they will become playable for you the next time you go to the start new campaign screen

It does more than just that. It also adds units listed on this page to the game: http://wiki.totalwar.com/w/Rome2_preorders The veteran hoplite merceneries, armored ram, and polybolos would be available to Roman/Carthaginian/Hellenistic players too. (I assume the other units listed will not exist ingame even for AI unless you get the DLC (since obviously those factions have much larger unit rosters than that (nested parentheticals are fun!))).

[Evan MF]

The DLCs are for user playability + expanded unit rosters, apart from the Nomadic Tribes which I think are a map extention (judging by the trade map showing the Nomadic regions walled off with forest). So I think all but the Nomads DLC won't affect an ongoing campaign game drastically.

[Ragga]

I've done DLCs for shogun and never had to restart

[AngryTitusPullo]

Base on previous TW games you don't need a restart but some new features will not be activated without the DLC. Seleucid AI faction will not have some new features if you continue your save games. Usually only a new campaign will activate all the new features as (I might be wrong) the startpost set ups were only taken account on a new campaign.