"Appropriating their powers" could be better phrased as "hoping to confer their blessings and also secure a significant PR boost."

The Mercian Register - a Tenth Century counterpart to the Anglo-Saxon Chronicle - recounts that Æthelred and Æthelflæd of Mercia led a military expedition to Danish-held Bardney in 909 (quite a considerable distance into 'enemy territory') to secure the relics of the Mercian St Oswald, and translate them to safety and a site of special significance at their new priory in Gloucester. The promulgation of Mercian saints' cults was a major part of the political strategy of Æthelflæd to gain Mercian support for her rule, and one that clearly worked very effectively, given her sole rule of the kingdom for some 7 years despite her Cerdicing origins and the pressure of her brother, Edward 'the Elder' of Wessex. A chapel to the local saint Bertelin was the central point of the new burh built at Stafford in 914, and, after the reoccupation of Chester in 907, the relics of St Werburh were translated from Hanbury, near to Danish-held Derby, to the safety of a new church within Chester's rebuilt Roman fortifications. Securing such relics was an effective way of demonstrating 'Mercian-ness' and appealing to the spiritual needs of the population.

I got my M.A. in Late Antiquity and Early Medieval Europe. IMHO by far the best source would be Peter Brown's book, "The Cult of the Saints: Its Rise and Function in Latin Christianity." It is short, clear, and brilliant. I cannot recommend it enough.