The moves leave the Mariners with 38 players on their current 40-man roster.
Romero, 25, was a 12th-round Draft pick out of Oregon State in 2010. Bawcom, 25, was acquired from the Dodgers in the Brandon League trade in 2012. He was a 17th-round Draft choice of the Dodgers in 2010 out of the University of Texas-Arlington.
Jones, 25, was a fourth-round pick out of Long Island University in 2009. Choi, 22, was signed as an international free agent out of South Korea in '09.
All four players would have been eligible to be plucked in the Rule 5 Draft by other teams if they hadn't been added to the 40-man roster prior to Wednesday's 9 p.m. PT deadline.
Players first signed at age 18 must be added to 40-man rosters within five seasons or they become eligible to be drafted by other organizations through the Rule 5 process. Players signed at 19 years or older have to be protected within four seasons.
In other words, an international player or high school Draftee signed in 2009, assuming he was 18 or younger as of June 5 of that year, needed to be protected this year. All college players taken in the 2010 Draft were in the same boat.
Clubs pay $50,000 to select a player in the Major League phase of the Rule 5 Draft, which will take place on Thursday, Dec. 12, during the Winter Meetings in Orlando, Fla. If that player doesn't stay on the 25-man roster for the full season, he must be offered back to his former team for $25,000.
Choi originally was signed as a catcher, but changed positions after missing all of 2011 with a back injury. He hit .295 with 18 home runs and 85 RBIs in 122 games this past season while splitting time between Class A High Desert, Double-A Jackson and the final few weeks of the season with Triple-A Tacoma. Choi played in the All-Star Futures Game for the World Team.
Jones spent most of the past season at Jackson, hitting .275 with six home runs, 45 RBIs and 28 stolen bases in 101 games and also hit .333 in four games with Tacoma.
Bawcom posted a 2.91 ERA with 21 saves in 51 appearances for Tacoma, striking out 64 batters in 65 innings, then recently finished a stint with Lara of the Venezuelan Winter League.
Romero missed the start of the season with a strained oblique muscle, but came back to hit .277 with 11 home runs and 74 RBIs in 93 games for Tacoma. The converted infielder was the Mariners' Minor League Player of the Year in 2012 when he hit .352 with 23 home runs and 101 RBIs in High Desert and Jackson.