Can i substitute frozen berries when the cheesecake calls for fresh?
The raspberries should work if you strain them thoroughly and fold them in very carefully so they don't break apart. Adding the liquid to the cheesecake will noticeably alter the texture, probably making it mushy; note that there aren't any water based ingredients in the recipe which you could substitute raspberry syrup for. I wouldn't recommend it. If you wanted to add raspberry flavor to a cheesecake, your best bet would be a raspberry pastry flavoring oil. If you didn't want to waste that liquid (and why would you,) just drizzle it on top of each slice as you serve it.