Short version: your car is OK with these tyres and rims.
What really is important for the car is the external geometry of the wheel.
How much of the wheel is the rim and how much is the tire can affect the comfort or the handling, but the car doesn't care.
Your 2 variants (225/65/R17 and 235/55R18) differ by 7mm or 8mm in diameter (in theory) for a ~70cm wheel. This is about 1% of the size. Tyres wear more than that before they need replacement and they are not made that much accurate in size in the first place. No issue here.
The width of the wheel can be another issue. If the rims have equal offset, this makes the wheel 5mm wider at each side. This may make the contact between the wheel and parts of the suspension or the arc more likely, when the suspension is deeply articulated and the front wheels are steered.
Most of the cars are engineered to tolerate way more wheel size variations - first, because not all 225/65R17 (or whatever) are made equal and second because of the possibility to use snow chains. Snow chains can add up to 30mm in each direction (and more if you are novice and don't tighten them properly).
In short, you may not be able to fit aggressive snow chains. Since you are asking the question, this is probably not an issue for you.
In most jurisdictions, you are not allowed to alter important parts of your car without a proper regulatory oversight.
These things are enforced to a different degree at different places.
Depending on where you are, it may be that no one cares. Or it may be the car to be considered non-road-legal and the driver fined if the required certificates are not presented.
Or something in between.