When you add something to the def 2 field, card 1 will have a blank front. Yes, it will still exist and it will still come up for review – the difference will be that the front will say –
Yes, it will still have its review history – that is actually the reason (one of the reasons?) that Anki doesn’t immediately delete cards that become blank. If Anki deleted the card automatically, the review history would be gone with it – whether you intended that to happen or not. It’s a high price to pay for a typo, right?
If the change you make causes cards to be created, then yes.
Try it. Fill def 1, card 1 is created. Fill def 2, card 2 is created and card 1 becomes blank. Empty def 2, card 1 is restored (with its history intact) and card 2 becomes blank.
The card – just like it says. And you’ll have an opportunity to preview everything on the chopping block, so nothing gets accidentally deleted. But deleting that card will also delete all of its review history.
When these blank cards come up for study, if you aren’t sure what you want to do long term, you can just suspend them.
I would say it’s a lot of trouble to go to. I think it’s more efficient to do the work up front to get everything you need into your notes and onto your cards. Do your research and make sure you’re addressing the common definitions to start with, rather than starting to learn in complete cards.
Then, in the rare cases where another definition sneaks up on you – of course you can add it to your note, but you don’t need to start that card over from New. When that happens (for me, it’s synonyms that sneak up on me), I usually use Set Due Date to make sure I see the active cards for that note in the next couple weeks or so, and I’ll remember the new definition or I won’t. If I don’t get it, I grade it Again, but a lapsed Review is a far cry from introducing the card as New with no history [especially using the FSRS algorithm].