To stay in ribbing you knit the knits and purl the purls, even when you inc or dec. So to change the flap to ribbing it would start like this -
CO 6. set up row k1, p1 3 times, (if you want 2x2 ribbing it's k2 p2 k2).
Row 1 (RS): kfb, work in rib to last st, kfb - that's where k the knits and p the purls comes in.
Row 2 (WS):work in ribbing.
Repeat these two rows until you have 18 (20, 22) stitches
Then work in pattern for 18, 22 or 26 rows for long earflaps. For short ones, do less rows. End with a RS row.
Follow the next paragraph about cutting the tail for the first flap and not for the 2nd one. Then you go into casting on for the lower edge of the hat itself. You will need a total number that's even for k1p1 ribbing or one that's divisible by 4 for k2 p2 ribbing. This includes the sts from the flaps as well as the number you cast on. The numbers in the pattern - 76 (84, 92) - would be fine, though they say to k2tog to join in the round. You don't have to join that way, but if you want to, then CO 1 more st. They also say to k2tog at the gaps where the earflaps are joined, but that's not really necessary. You can take the tails from the one flap to close any holes there might be.
Then just knit in your rib pattern. On Dec round one, it works to do 6 sts in the rib pattern, then you can p2tog or k2tog, depending on 1x1 or 2x2 rib.