Substitutions need to be accounted for. For instance, if you add 100g of strawberry puree, you need to look up strawberries on the USDA website and see how much fiber, sugar and water they contain. Then you reduce the flour, milk and sugar accordingly, so that you still have the same quantity of liquid, flour/fiber, sugar, etc. Then after that, sometimes there are effects from pH and/or a change in the degree of saturation of fats, it can be a lot to deal with.
For what it’s worth, I tried to make a strawberry cake from scratch a number of years back, with a number of different substitutions, and in the end nothing was as delicious as a classic white or yellow layer cake sandwiched with fresh strawberry puree as a filling. It was very difficult to get much strawberry flavor into the cake, while the puree as a filling packed loads of flavor.
Things like extracts or zest are easy to add without worry, instant coffee shouldn’t be a problem. But lemon juice might require some baking soda to get the batter to set at the right point in the baking process, and the soda will neutralize the juice so that it doesn’t taste so bright and lemony, so the solution is to syrup the cake after baking with the juice so it remains fresh and bright.