Factions & Tourneys (Anything orange to you) you should be able to cast Strength, Agility & cunning on ur enemy as of right now you can't it says you can't perform those kinda acts. Reason for this is because Since MindBlast is a very useful spell when done right you should be able to raise the persons strength or Int and lower their lowest stat to make a bigger gap so Mind blast does more damage, as it is right now you can only lower their stats.
The mechanics of Factions strictly prohibit any beneficial actions to be used upon a factions player, unless the player attempting to do these actions is within the same faction. This is in place to prevent outside interference in factions (cross healing, etc). That being said, you will not be allowed to perform any beneficial acts on an opposing faction member, whether that be healing, curing, or casting beneficial stat-buffs (Cunning, etc). You (should) be able to use this technique on other enemies, such as warring guilds or Order/Chaos opponents, but this will not work for Factions.