Normally, the Enchant Item ritual only allows one to enchant items within their power level. Some enchanters however are able to create surprisingly powerful artefacts. To do this however, the ritual caster must supplement the standard components with his will. Doing this requires sympathetic catalysts, special reagents which are tuned to the abilities with which you wish to imbue the item. Identifying and acquiring the necessary components may be an adventure in itself.
In game terms, if you want to enchant an item up to 5 levels higher than your character, you will need to complete a minor quest to get all the necessary materials. Further, such item will replace an appropriate treasure parcel for the current or one of the next two levels.