UCLA Double major in two different colleges

Hi,

I was accepted into Henry Samueli School of engineering this fall as a bioengineering major. I have now changed my mind and decided to double major in Neuroscience (offered in the college of letters and sciences) and Computer science & engineering. I really want to attend UCLA, but one of the representative at the BruinBound event said it is nearly impossible to declare a second major in a different college other than the one I was accepted into. I want honest opinions from current students. Is it really that difficult to declare a second major in a different college? Also, is it difficult to change major within the same college (Bioengineering to Computer eng.)?