As part of the deal, the White Sox will pick up most of what remains of Alomar's $2.4 US million salary.
Alomar is scheduled to become a free agent at the end of the season.
Alomar is hitting .287 with seven homers and 25 RBI in 51 games this season. The 36-year-old is a career .275 hitter in 15 seasons with San Diego, Cleveland and Chicago.
The Rockies and White Sox are playing in the Hall of Fame exhibition game Monday afternoon in Cooperstown, N.Y.
Pacheco, 23, is 2-2 with 16 saves and a 3.16 ERA in 41 games with Class-A Salem this season.
The White Sox are also expected to recall third baseman Joe Crede and catcher Josh Paul from Triple-A Charlotte in time for Tuesday's game in Minnesota.
