Just like with the Psychographics and Donut Ruling, the Runner cannot use to install an with 10 power counters on it by spending 0. As an install cost, the amount of credits actually paid is what determines the value of X.
If a Runner uses Eureka! and reveals Angel Arena, can they set X to 10 and then use Eureka!'s effect to install Angel Arena with 10 power counters, without spending any credits?