The effects of Attributes, Abilities, Talents and Traits can't be modded in D:OS 1 directly. That's one of the biggest limitations, unfortunately. Baardvark (author of the mod Scales) tried his best to make sneaking viable in EE. Reducing AP cost by the Sneaking talent is impossible.
You can download his mod from Nexus and have a look into the 'Base' char script (Data - Public - Shared - Scripts) and into the 'Potion' file (Data - Public - Shared - Stats - Generated - Data) which contains the sneaking buffs scripted in 'Base'.
We all want to sneak as we once did in recent times but, sadly, we can't...
