Carrasco was on optional assignment with AAA Buffalo at the time of this call-up, so he was already on the Mets' 40-man roster. He has spent (approximately) 48 days on optional assignment in 2011, so the option year will officially count as his third and final. This call-up, as well as any subsequent 2011 options and call-ups, will have no effect on the number of options he has remaining. Following the 2011 season, Carrasco will be out of options.
Thayer heads to AAA Buffalo on optional assignment, and thus remains on the 40-man roster. Prior to his May 27th call-up, Thayer spent the first 57 days of the season in the minor leagues. However, he was not on optional assignment at the time (he was simply on a minor league contract), so it didn't count toward the 20 days he needs for 2011 to officially be marked as his third and final option year. That clock starts now.
This transaction has no effect on the 40-man roster, as both players involved were already on it. It's worth noting, however, that this move restarts DJ Carrasco's ML service clock, which had been frozen at 4.166 years (read: 4 years, 166 days). Once he earns 6 more days of service time, he'll eclipse the all-important 5 year mark. With 5 years of ML service come certain rights, including the ability to refuse any minor league assignment, optional or outright, and force the Mets to either reinstate him to the active roster or release him and continue to pay out the remainder of his contract. In other words, Carrasco is now (or, technically, in 6 days will become) very likely to remain on the Mets' active roster (or DL) for the remainder of his contract (which runs through 2012).