This was the first time a non-Cistercian had become abbot at Melrose, and moreover, the pope granted Blackadder leave to take the abbacy without becoming a monk.
In 1477 Blackadder's name is recorded in a letter of Pope Sixtus IV, where it is said that the pope had received a petition from "Robert Blakidir", a rector of the church of Lasswade in the diocese of St Andrews, requesting permission to build a hospital near the church.
Twenty years earlier, in 1472, a papal bull of Sixtus IV elevated the Bishop of St Andrews to Archbishop.
It was Blackadder's predecessor at Aberdeen, Thomas Spens, who in February 1474 raised the first significant opposition by obtaining lifetime exemption from the jurisdiction of St Andrews over either himself or his diocese.
Moreover, Blackadder had the sympathy of the king, James IV, who himself was worried about so much power resting in the hands of one bishop.
Letters to the pope were sent by the king and the Scottish parliament, requesting that Glasgow be given the same status as the Archbishopric of York.
In September 1491 he went to France with Patrick Hepburn, 1st Earl of Bothwell and the Dean of Glasgow to renew the Auld Alliance.
[4] On 24 August 1495 he arrived at the court of King Ferdinand II of Aragon and Queen Isabella I of Castile.
A letter, dated 12 September that year, was written by these monarchs to the pope urging that Archbishop Robert be made Cardinal.