1) By getting more power points, which he gets by getting more magic.
2) Nope. Have to increase Magic, or possibly learn it as a metamagic if a certain optional rule is in play. Either takes time.
3) Nope. The points of Magic you commit to power points stay as power points, and the ones you commit to mage stuff stay there. When you get a new point of magic, you must decide which it goes to.
The closest things to on-the-fly stat change for Adepts are Boost Attribute, Berserk, and I think maybe a couple others.