What are the specific mechanics of a rogue’s use magic device ability?


Imagine a homebrew weapon, for example, a dagger that behaves like a normal +1 dagger to everyone except elves, who are conferred an additional bonus as well other abilities or effects.

When a rogue uses any given magic device, how does this work? Is the rogue effectively "emulating" a certain combination of race/class/level, in order to coax magic out of the device? Or is the rogue simply ignoring or bypassing restrictions to use a magic device?

In the specific case of the above dagger, the weapon has no requirements that prevent anyone from using it. However, if the rogue is effectively presenting itself as an elf to the weapon, it might expect to get the bonus. Given that the description of UMD doesn’t really address this specifically, how does this rule?