Se o conteúdo do arquivo data
for
0500 * * 1 ( 02-StartFix.sh)
1850 * * 1 ( 02a-ResetFlag.sh)
2000 * * 1 ( 03-StopFix.sh)
2005 * * 1 ( 04-DssEOD.sh)
então
sed -i -r '/02a-ResetFlag.sh/{s/^([0-9]+)(.*)$/9999/g}' data
irá modificar o arquivo data
para
0500 * * 1 ( 02-StartFix.sh)
9999 * * 1 ( 02a-ResetFlag.sh)
2000 * * 1 ( 03-StopFix.sh)
2005 * * 1 ( 04-DssEOD.sh)
testado em GNU sed version 4.2.1