@ucbalumnus lil bit misleading there. Applying as English at UCSD won’t make you more likely to be accepted than if you’re applying as a CS major, UCSD admits without considering that.
(Of course, if your personal statement reflects your passion for English, you’ll be in slightly better shape. However, then you’ll be admitted as an English major and will have to get the 4.0 in continuing courses to be admitted to CS.)
But in the overall admissions process, marking CS won’t hurt you, you’ll just be admitted as undeclared if there are stronger CS candidates.