I would probably go with defensive powers (resistance to magical influence - to allow his wearer to always make choice of his own free will), something like aura of courage (to inspire his people in dire situations), or maybe even Aura of Authority if you want to go towards something more intimidating or forcing respect. Maybe good health (bonus to aging roll, recovery roll and such). Wisdom in the form of bonus to Folk ken rolls and other social abilities or even knowledge skills could simulate divine inspiration - again, the King will make is own free choice, but he has a bit more information at his disposal. Does he use it wisely, can he interpret correctly this extra information ? it is still up to him to show the (right) way.
I find these kind of powers suitable for a Divine power driven by peace and care.
Instead of allowing him to turn into a dragon, allow him to command a dragon. It could be an ennemy of his ancestors who was defeated and bound to the family to do his biding until release - possibly as a Divine reward for the King and Divine punishment for the Beast. Thus the dragon can be of any origin itself, even if the biding is Divine.
You could even add a clause to the biding: "Would the King call the Great Beast for selfish purpose, The Beast would be free to exact revenge for her centuries of servitude". This kind of little "fine prints" in the contract would explain why past rulers have been so reluctant to use it (thus becoming part of the Legend instead of a "certified threat") and also give an opportunity for the players - would they end up on the wrong side of the King - to try to use the loophole by turning a rightful summoning into a selfish request by tempting the king into using the dragon when he would not really need it or for unjustified need (like crushing enemies after they surrendered).
Again, if used properly, it makes the king very powerful as long as he is acting with virtue but it does not make him virtuous or divine. He is not an agent of God doing his plan, he is still human with his weakness, thus can fail.
Based on Wikipedia summary of Andrew II, his reign was not really great (crusade's failure, issues with the nobility, conflict with the pope...). So you can either depict him as a good guy, surrounded by mischevious consellors and corrupted (not necessarly infernally corrupted though) vassals - maybe aware of his predicament he is reaching through outsiders for help and support - the magi. Maybe the real crown was stolen, replaced by an imitation and without her blessings, he cannot distinguish friends from foes. Maybe the Crown lost Mary's blessing due to past action/deeds which the King need to amend for (was it his own action, his father or another ancestor is up to you to decide).
Or the opposite, he has so much trouble because he is vain, concern by his own well-being, but very capable. The failure he is facing are only due to some guys - who saw through his charming facade - and want him to fail so he does not settle as a ruthless tyrant. By fostering constant troubles for Andrew, his enemies deprieve him of opportunity to solidify his power by distracting him from his great master plan.
Finally, is the shapeshifting ability a boon or a curse ?
History/legend report it as a gift. But what if it was a curse ? "Thou cannot serve two masters" (and since God's will cannot be fathom by men, you might not need to find a better explanation). Another reason why the magi could get involved: how to lift the curse. Maybe invading part of Rus was against God's will, thus the curse. To remove it, not only does he need to decide to rule only a part of his lands, but he must find the rightful heir for the part that he will abandon.