Question for Robby and Steve on conscience

I probably should be concerned that Steve Shiffrin and Robby George are united in disagreeing with my assertion that liberty of conscience should not empower a justice of the peace to refuse to marry a same-sex couple in a state where such marriages are legal.  So I'll take it from a different angle: to what extent is your support of the justice of the peace's right of conscience in this scenario freestanding and absolute, and to what extent does your willingness to recogize the right of conscience flow from the fact that the rules of the game have changed while the person is already on the job?  Suppose that Massachusetts advertises for justice of the peace openings by notifying applicants that

"Justices of the Peace have the duty to solemnize the marriages of all applicants who meet the statutorily prescribed criteria for marriage.  This includes same-sex couples." 

Should I be deemed qualified to serve as justice of the peace even if I state my categorical refusal to marry same-sex couples?  In other words, when does the liberty of conscience become a license to rewrite one's job description?

And Robby is correct that SSM laws are certain to affect individuals and groups beyond the participants in those marriages.  Those who insist otherwise are being naive or disingenuous.  That's why strong religious liberty protections are so crucial, but I do draw a line between protections that eviscerate the state's ability to effectuate its laws through its designated agents, and protections that prevent the state from effectively designating all market providers as its agents.