It’s officially a done deal. The Cowboys have exercised Byron Jones‘ option for 2019, according to Todd Archer of ESPN.com (on Twitter). The move was actually formalized on Friday, but was not reported until Monday morning. 
Jones will be moving to safety from cornerback this season, but his salary will reflect his former position. The Cowboys now have the defensive back under contract for $6.2MM, though his salary is guaranteed for injury only.
Jones, 26 in September, has started every game for the Cowboys over the last two years and has tallied 130 tackles, two interceptions, two forced fumbles, and one touchdown in that span. Last year, his performance dipped a bit, as evidenced by his 76.8 overall score from Pro Football Focus (ranked No. 54 amongst safeties), down from 83.7 in 2016. The hope in Dallas is that he will get back on track at cornerback.
Since the fifth-year option was implemented under the new collective bargaining agreement, the Cowboys have exercised the additional year on every first round pick except for Morris Claiborne, the No. 6 overall selection in the 2012 draft.
You can keep track of all fifth-year option decisions using PFR’s tracker.