I suspect "warm" is meant to maintain temperature, rather than raise it. My crock pots are too ancient to have anything other than "high" and "low", so I can't assert any real authority. However, if you reach 145F within the first hour at the highest setting, then keep it at "warm", and test the temperature after about 30 minutes with an instant-read thermometer and it stays around 140-160F, you'll probably be fine. Personally, I'd test the temperature first by cooking water.
If the temperature stays above 140F at low, the worst risk you'll have is overcooking. Beans and vegetables like carrots and celery can overcook fairly easily in a crock pot, but higher collagen meats meant for stews tend to be fine when cooked for extended periods. Most crock pot recipes for stews and soups usually hold fine when at low for a full workday, although that's presuming a somewhat 70s-era soup aesthetic, which is probable for a crockpot recipe.
However, I would be inclined to attempt the recipe using the low setting rather than reducing it to warm, if you're not going to test the temperature first. If it turns out to be overcooked, you can always puree the ingredients with a blender...
I also doubt that switching to "warm" would be dramatically less likely to overcook the food than "low", unless it holds at a pretty stable 140F, and low ends up somewhere around 160F.
Best Answer
Bone broth is supposed to be cool when you add the vinegar to it. And then it's supposed to sit up for a half hour or so in order to let the vinegar draw the minerals, etc., out of the bone. So really at the time of this writing you've let the stock, which has already had all potentially harmful micro-organisms neutralized by way of boiling, sit up for just a few additional hours. On top of that, in order to make a good poultry bone broth you're going to bring it all to a boil again and let it simmer for another 24 hours. There's no chance anything bad is going to survive that onslaught. And there's no way mere stock, fresh off its cool down cycle, has had a chance to take in any new micro-organisms capable of forming the kinds of toxins which aren't resistant to such treatment. You're fine. And hats off for going paleo!
[EDIT]
By saying that the stock hasn't had a chance to take in any new micro-organisms capable of forming the kinds of toxins which aren't resistant to such treatment, this really is to acknowledge that some micro-organisms cannot be destroyed by boiling and, as pathogens, are the by-products of bacterial growth; since your stock has not had the time/opportunity to engender or accommodate bacterial growth, (thus the term new), there can be no reason to anticipate a consequent whose known antecedent is lacking. No new bacteria, no possibility of new toxins ...unless introduced from some flukish or otherwise uncommon manner of uncarefulness, (a cat's paw?), which would be a whole other matter. It is almost always possible to imagine contingencies which, for their very particulars, disallow of what would normally be sound advice.