Of course you can switch SA's! My heart goes out to you Kou! I know it seems impossible but, it's NOT! Stand up for yourself! If you like that store (where is SCP? Sorry, I don't know all the abrevs.), and you want to stay there, then CHANGE SA's!! The idea of working with the same person is to help YOU not to help THEM! And this SA just sounds wrong for you. I'm not saying they're bad, or unprofessional...it just feels, to me, that the two of you do not communicate with each other. You should never leave a store of Hermes quality and reputation confused, or anxious. It should be a pleasure to walk in the store and buy things.
And the fact that you are having such trouble really concerns me. Please, please, change SA's. NOT to "punish" your current SA, but, for your own comfort. And if you can, discuss this with your current SA. Let them know that although you appreciate their knowledge and passion, you just don't feel like you are working together to get the things you need and that you'd like to try working with someone else in the store--to keep your relationship IN that store. With the amount of money you've dropped there, they should be thrilled to find someone else to keep you there!
My two cents.