Is this as problematic as I think it might be? "Text" only includes what's in the text box, right?
It might be broken. I mean, using Terramorphic Expanse to pop out Iona, Shield of Emeria or Primeval Titan to bring out anything you want is just very good.

Wait, would the Terramorphic Expanse example work? There aren't exactly Basic anything but land, and you could only replace land, right?

I think you're right about terramorphic expanse. I expect there are some other broken shenanigans, but I'm not sure what (there are lots of examples that would be very useful, but are not unreasonable for two cards).

I'm not sure if it can be templated well or not. It should probably allow you to re-choose targets if a spell targets, but that means if a spell targets you can only play it if it has valid targets, even if you intent ot change them later.

Edit: the most broken thing I can think of at the moment is Leyline of Singularity.

Text in the context of "changing text" (that's a lot of text) includes card type, so this can actually change card type. If you change something to instant, there you go...an instant on the battlefield!

It also allows you to play duplicate planeswalkers, and if you replace an "instant" on the stack with "enchantment" (or, for that matter, "land"), then when it comes time for that spell to resolve...yeah, the game blows up.

Some Questions:
1. If it could only change permanent types with other permanent types, would it work?
2. What if it somehow changed the card while it was still in your hand, rather than on the battlefield or stack?
3. Is Leyline of Singularity broken because it turns everything into a certain card type? Say, creature?

For leyline, I meant, turn all non-tribal permanents legendary instead of all non-land, cutting off your opponent to one or two basic lands.

Gotcha.

Heee. I tried this a year ago, with Twist the Form. It works okay if you restrict it to permanent types. Changing creature to instant or vice versa leads to a lot of problems.

In playtesting, it's mainly used as a Remove Soul/Pacifism, by turning some random creature or creature-token-maker into making useless planeswalkers instead.

I made it with the primary intent of letting you search for different things that specified by a card's text. As in, making Fabricate search for planeswalkers. Obviously, it would have multiple uses.