One Coin's code operating with the old blockchain of another coin

Can one coin read the blockchain of another coin?

Let us say you have a coin that needs the functionality of another coin.
You change it to the code of another coin except with chain parameters matching the old coin.

Let us say, you had a dash based altcoin and you changed your code to match let us say bulwark.
Would the new bulwark based code (proper chains parameters) be able to read the blockchain and move forward?

Or does the blockchain have to be modified first?
If that were the case, in theory, a coin-swap is simply modifying the old blockchain to work with the new coin software.
So, in theory, one could swap one blockchain to be modified to work with another, right?

The final choice (as a novice thinking) would be to be able to read both coin's "file formats". If it is the old format read it this way, if it is the new format (after block x) write it this way.