The base ability of the Magus Arcane pool class feature is.
At 1st level, a magus can expend 1 point from his arcane pool as a swift action to grant any weapon he is holding a +1 enhancement bonus for 1 minute. For every four levels beyond 1st, the weapon gains another +1 enhancement bonus, to a maximum of +5 at 17th level. These bonuses can be added to the weapon, stacking with existing weapon enhancement to a maximum of +5. Multiple uses of this ability do not stack with themselves.
At 5th level, these bonuses can be used to add any of the following weapon properties: dancing, flaming, flaming burst, frost, icy burst, keen, shock, shocking burst, speed, or vorpal.
Adding these properties consumes an amount of bonus equal to the property’s base price modifier. These properties are added to any the weapon already has, but duplicates do not stack. If the weapon is not magical, at least a +1 enhancement bonus must be added before any other properties can be added. These bonuses and properties are decided when the arcane pool point is spent and cannot be changed until the next time the magus uses this ability. These bonuses do not function if the weapon is wielded by anyone other than the magus.
So my question is. If an item is already enchanted to +10, lets say +1 Dancing Vorpal, can a Magus Increase the enhancement bonus to +5 to make it a +5 Dancing Vorpal Sword for a total of +14 temporarily.