If you like fruit wine kits, it might be safest to keep purchasing the ones you like. I think that taking a chianti kit and adding fermentables and fruit flavors might just unbalance the kit, and be weird. Maybe a merlot with blackberry flavoring would be ok, but adding extra fruit would boost the ABV of the kit, so you might end up with blackberry rocket fuel. I don't think any decent commercial kit would give you the results you're hoping for, except for the Island Mist kits or the Breezin' kits.
If you want to do a homemade fruit wine, though, there are lots of recipes around for that and usually cheaper than a wine kit.
You could do a mini experiment to see how this would work, just by buying a commercial bottle of wine and then adding fruit flavor to it. That would mimic what you're thinking of trying.
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