Some of these are game-breaking. There aren't TOO many unbalances with the units.
However, there are a couple of things I would do. Of course, I haven't done it yet, as I have to make AI strategy tips, as well as learn to make new units, instead of modifying existing ones.
Change #1: Global Warming produces Tundra (1

, 1

, can be improved if adjacent to a river), instead of desert.
Change #2: Ironclads are 16

units, with alot bigger cost, and +100% defence in coast. Same speed, and still can't move into ocean. Upgrade to Battleships. That said...
Change #3: New unit: Steam Ships. 20

units, that can move faster than Ironclads, and travel over ocean. These can eat Frigates and Ship-of-the-line for breakfast, lunch and tea, but are no match to beat fortified Iron-clads.
Change #4: New unit: Modern Privateer. 26

units that can destroy un-guarded transports, and pillage and blockade like a regular privateer. They are the same speed as battleships. Now... I KNOW that that is NOTHING like real life ATM, however the reason is this: Pirates exist, but no government wants to hire them (like they did in the medieval era). Modern Privateers will also have a (low) anti-aircraft value.
Change #5: Unlike most people, Im NOT moving the time of Airships. That said, I am pulled between two choices:
A) Flak. Comes with Artillery (before Rocketry), and acts as good anti-air, albiet with VERY low strength, but a HUGE anti-airship value
B) Airships cannot attack, only recon. But they have more Line of Sight, and don't obsolete.
But that is minor. Personally, I don't care losing 10% of my strength in a war... its small change! Add on the fact that airships lack collateral damage abilities, and you mean that Airships are useless to try and suppress my SoD... and even in city walls they are nearly useless. But B is also very realistic!
Those are my planned mods... when I get around to it. But ATM, they are tiny problems. I do miss late-game privateering however...