Mercedes says it accepts the International Tribunal decision, and thus won’t appeal against it.
Given that its own lawyer suggested the punishment – a reprimand and ban from the Young Driver Test – that is perhaps not surprising. The team issued a statement this afternoon, which reads as follows:
“The MERCEDES AMG PETRONAS Formula One Team acknowledges and accepts the Decision of the FIA International Tribunal published today.
“The Decision of the International Tribunal confirmed that the team acted in good faith regarding the Pirelli Tests, never intended to obtain any unfair sporting advantage and had no reason to believe that approval for the Pirelli Tests had not been given.
“Mercedes accepts the proportionate penalties of a reprimand and suspension from the forthcoming Young Driver Test that have been decided upon by the Tribunal.
“Mercedes would like to once again restate its firm belief in proper due process and commend the FIA for the principle of an independent disciplinary body.
“The team would furthermore like to thank the International Tribunal and its President for the fair hearing it received yesterday.
“In the best interests of the sport, the team does not intend to avail itself of any right to appeal the Decision.
“Mercedes looks forward to working with the FIA and its fellow competitors to establish a more rigorous procedure for testing in the future, particularly to support the appointed tyre supplier.
“We now wish to bring this matter to a close and focus on the forthcoming British and German Grands Prix, both of which are important home races for the team.”
Adam Cooper F1 
Of course they won’t appeal. Merc would open themselves up to receiving an actual penalty instead of the finger wag that they got. They are thumbing their noses at FIA and the other teams, knowing that they avoided any meaningful punishment.