I'm pretty sure assassin would be an advanced specialization, and rogue would be the base class. Meaning assassin likely has a level cap of 10, while rogue has 15. Similar to how a barbarian, or fighter would be base for a fighter. You may want to include some gear of the sort that would allow you to obtain a disguise, or have a skill level that would work as a disguise otherwise people would likely attack you on sight being undead. Otherwise I don't see anything specifically wrong with it.