No, you don't add stitches, or I think the pattern would tell you to do so. Take Kristen's Palindrome scarf. I took off one repeat,because I want this scarf to be skinny. This left 28 stitches, each row is 28 stitches with no increases. As if by magic, it all stays straight.
Of course, I've only made two cabled things, so somewhere there might be a pattern different from this.
BTW, we ARE neighbors! Have you ever been to Boersma's Yarn in McMinnville? Great little shop.