[Skarg]

Cidri is interesting in that it both says:

* it can hold anything you can imagine, so in that sense yes if someone wants Yrth on Cidri they can have it be there.

but also

* ITL specifies many things about the "known" Cidri that also refer to an immense "known" context that says things like "99% of the wizards on Cidri are members of the Wizards Guild, and the rest used to be" and other wide statements of homogeneity a particular way.

And, Yrth is both similar in some general ways, but in many specific details is very different. The races are rather different flavors even if they have similar names. The magic system and known spells are rather different. There are no world-spanning guilds or gate networks, and the creature catalog is quite different.

I think it'd be easier to play Yrth using TFT rules than to try to locate it on Cidri, but you could certainly do so. When I adapted my original TFT campaign to GURPS, it raised a number of interesting questions with all the specific differences and which things I wanted to change or say were different in one part of the world versus another.