If im a ninja and all the sudden decide i want to be a warlock or samuri after a while will i lose the ability to do certain things or spells that i aquired from the other role? Granted i might not be able to use ninja stuff with a warlock but will my other stuff go down and i wont be able to use swords again etc?

It seems so far when I have changed classes that you aren't able to use class specific armor items unless you are currently that class. i.e Assassin's cowl, ect. Also, spell casters can't wear most of the warrior class armor except for low level items (trousers,seude boots, ect) Weapons are pretty much restricted to you first being able to learn the skill and if the weapon has a strength requirement, because once you learn it even if you just have level 1 you can improve that skill through the Guilds or as you level up. Just remember until you get your new class to the same level as your highest level class you progress in your skills VERY slowly. I used the Dragon arrow cheat with one of my characters having the merchant skill and a decent Will score to rack up some quick gold so I could buy some of my skills to the next level each time I advanced in my new class. As far as spells go you don't lose any that you have learned but if you change classes and the class you change to doesn't have those spells as learnable then you are able to learn the other spell classes at HALF your level with that spell class(Moon,Fiend,Spirit ect.) Hope this helps