Adding fruit after fermentation is started

I started a batch of peach wine and the yeast has been working for about 24hrs...I'm now finding out that peach needs some extra "body" whether it be grapes or adding raisins...Is there any way I could add a little bit of "body" after the wine has already started to ferment?

Since it has only been about a day you can cut/mash up the fruit and add it into the primary fermentation vessel without many worries. Just make sure you are sanitary with it.

You can also add during the secondary fermentation although that may not give much body body it will add the 'essence' of the fruit or whatever aromatic you use.

What would you use? I have some fresh concord grapes...But the recipes I've found use either raisins or white grape concentrate...

Personally I would stick to white raisins since the raisins are a go to in a lot of recipes and add a subtle character.

My dandelion wine is like that- it's pretty thin without adding white grape concentrate or raisins. I simply buy the "golden raisins" and chop them up a bit (it's a HUGE PITA!) and add them to secondary and rack the wine on top. It works very well.

You can always add stuff whenever you want. There isn't really a window of time when it's too late to add raisins or grape concentrate as long as you still have some active yeast. If you add in secondary, be careful to watch for foaming up. Since the fermentation will restart, you may not want to top up your carboy until the major foaming has stopped. Then you can top up as usual.