During riveting of the connecting link on a new motorcycle chain (DID525VX), I accidentally overpressed the link's plate by 1mm. I'm wondering if it's a big deal and I should replace it, or I can continue riding with that overpressed link?
I'm not sure what the consequences of a chain failure are on a motorcycle, but at least on a bicycle (having experienced a chain failure on a bicycle), it's not nice to have your chain to fail! It will hurt, because it fails when pedaling hard, so you might lose balance. On a motorcycle the chain speeds are much higher, so the way it might hurt you could differ.
Not only that, but at least your journey will end when the chain fails.
I agree you should not continue driving with your chain in the present condition.
However, a slight disclaimer: as my experience of chains is from derailleur bicycles, I might be a bit too careful here. Derailleur bicycle chains are very small for the job they do, everything is as miniaturized as possible to fit as many gears into the system as possible. On a motorcycle, not having derailleur gearing, the chain can be much larger and thus the error margin is better.
I think your biggest problem is going to be the squashed X-rings. They are meant to be squished slightly so that they form a good seal with the metal plates, but an extra mm is going to crush them. They will likely crack or degrade very quickly, allowing the chain lube to exit and dirt and crud to enter.
For the cost of a new master link, I would start over and try again.