Change logging level programmatically for multiple jobs
The logging level is held in the command column of msdb.dbo.sysjobsteps. By editing the command you can set the logging level you require.  There is a system stored procedure - sp_update_jobstep - to achieve this.

From a quick look on my local system, SSIS job steps' commands seem to be a reasonably straight-forward concatenation of labeled values. A bit of regex and some substitutions should be sufficient.