Paradox and Tantalus have indeed added a lot of great stuff to the game over the years and made many welcome changes, though of course a few not so welcome ones...
Overall I really like the game as it is, but there are several things from before one particular big patch I wish they hadn't changed and wish I could get back - they completely changed how your (or any other empires') borders change and how you capture most systems and changed many mechanics in the game, in particular related to combat and introduced war exhaustion etc...
As said, I rather like the game as it is, but do wish we could go back to certain older mechanics or even "God" forbid be allowed to choose which changes to add or not, at least in single player, but it is what it is...
Also I'm quite lucky to have two PS4s, one in my house and one in my girlfriend's house and when that big patch came out, I patched one install of the game and started playing with the new content almost immediately, however I intentionally didn't patch the other install for months until I had finished a particular playthrough under the old mechanics and indeed whenever there is such a big patch, where old saves aren't compatible, I still generally wait months until I'm finished whatever playthrough I'm currently on before patching on at least one of my consoles
...
Anyway as others have said, unless you have old installs of the game on one or more consoles or harddrives, there's no way to play the original unpatched version of the game without the game on disc!
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