Once you change, you're not guaranteed space on your original flights if you misconnect. Anything could change between now and then, and inventory can be eaten up after you make the change.

So worst case is not you get back on EWR-IAH-LAX, rather worst case is you get stuck overnight in EWR because everything else is full after you spend all afternoon unsuccessfully trying to standby for flights after having given up your original, confirmed booking.

Out of a hub like EWR, flights can fill up quickly. All it takes is a bit of a backup at EWR, and inbound connections get hosed, and then later evening flights start filling up quickly as people get protected and rebooked.

If you're not checking bags, I would try to standby/SDC after arriving in EWR to play it safe. Had the 1:10 been a bit longer I would've just SDC'ed it earlier, but 1:10 is too risky, IMO, to give up confirmed space afterwards. Also, you don't want to blow $25 for the late flight given that you really want the earlier one.