Suggestions:
HD d6
Keep the combat styles, spells, and Ranger class ability progression (including Evasion at 9th level).
6 skill points/level, Rogue BAB & Rogue weapon proficiencies, Ranger skill list + Disable Device, Open Locks, Bluff, Sense Motive.
Or, these weapons: all Simple plus hand axes, shortswords, short bows and kukri.
At first level: Trapfinding, Track, Wild Empathy, and Favored Sneak Attack (+1d6 SA damage, but only vs. favored enemy).
At 3rd level, grant +1d6 regular Sneak Attack. Stacks with Favored SA when fighting Favored Enemy.
At 5th level they'd get +2d6 Favored SA, and a new Favored Enemy (still only +1d6 regular SA).
At 7th level, +2d6 regular SA (and still +2d6 Favored SA).
At 9th level, +3d6 Favored SA (and still +2d6 regular SA), and Evasion.
At 10th level, extra Favored Enemy.
At 11th level, +3d6 Favored SA / +3d6 regular SA.
12th level: Rogue Special Ability.
At 13th level, +4d6 Favored SA / +3d6 SA.
At 15th level, +4d6 Favored SA / +4d6 SA, and pick a new Favored Enemy.
16th level: Rogue Special Ability.
At 17th level, +5d6 Favored SA / +4d6 SA, Hide in Plain Sight.
At 19th level, +5d6 Favored SA / +5d6 SA.
20th Level: Rogue Special Ability, 5th Favored Enemy.
-- N