Help with importing a texture

[Labiathan]

Alright, so I'm trying to import a texture that, I'm guessing, Is a model off of the raise dead model, even if it isn't, we'll use it as an example.

I know exactly how to import this, I've done it before, but this model says "Will Overwrite default texture" And I'm wondering if that will Overwrite the raise dead spell effect and make it into that. Is this true? If not, what does Overwrite default texture mean?

Thanks in advance