Depending on the temperature in your fridge, cooked lentils will be safe to eat for 2 to 5 days when using a sealed container, filled with the cooking water. By immersing them, your lentils won't dry out and they'll be ready to use whenever you need them - just drain the amount you need.
If you've got sufficient freezer space you could also freeze the cooked lentils. Just prepare a whole lot of lentils and divide them in individual portions to put in small freezer bags. Make sure you push out any air before sealing the bag. Freezed lentils will be fine anywhere from 4 up to 6 months.
However, I would strongly recommend using dried lentils, which I'm sure you'll be able to find in Copenhagen. Just make a habit of soaking the amount of lentils you need for your breakfast and you'll never have to worry about storing leftovers. It's a lot cheaper too! But above that, dried lentils tend to taste much better than canned lentils. :)
I do not have any information on the change itself, but neither does that claim in Wikipedia.
However, I would refer you to the discussion page of lentil's and read over the community's discussion regarding the article's nutrition claims generally. They are not pleased with many of the claims, and have been active in moderating it. Also of note, the claim has no citation.
Upon my reading, I would not take for granted that the minor act of sprouting in water changes nutritional value substantially, especially as compared to deep-frying them or other processes.
That said, you might refer to the general sprouting article:
These nutrients are essential for human health. To clarify, the nutritional changes upon germination & sprouting have been summarized below. Chavan and Kadam (1989) concluded that - “The desirable nutritional changes that occur during sprouting are mainly due to the breakdown of complex compounds into a more simple form, transformation into essential constituents and breakdown of nutritionally undesirable constituents.”
It goes on to explain that, according to studies done by Chavan & Kadam (1989), Cuddeford (1989) and Shippard (2005), changes during the sprouting process result in:
- Increases in protein quality
- Increases in crude fiber content
- Increases in essential fatty acids
- Increases in vitamin content
The article cites a claim from the Shipard (2005) study: "“When seeds are sprouted, minerals chelate or merge with protein, in a way that increases their function.”
Best Answer
Lentils are good for a long time: Many claim that they stay safe "indefinitively".
While that is clearly an exaggeration, properly stored lentils stay edible for years if you keep them well-sealed in a cool, dry and dark(-ish) place.
Note that dry storage keeps mold at bay, closed jars protect from insect damage and cool temperatures slow trace amounts of fat getting rancid. They might get tough and a bit stale, but that can be mitigated by cooking longer and a generous hand when seasoning.
To add one source (for completeness):
Still Tasty gives one year but states that it doesn't get unsafe, simply looses taste.