How to clear SQL Agent Job Scheduler Cache
You may use below script to alter the schedule:

EXEC msdb.dbo.sp_attach_schedule @job_id=N'533fb186-72e9-40c5-af88-c8e57f097126',@schedule_id=16
GO
USE [msdb]
GO
EXEC msdb.dbo.sp_update_schedule @schedule_id=16, 
        @active_start_time=24500
GO


you may find job_id using below script for the job you want to change schedule:

select job_id from msdb..sysjobs where name = 'SomeDb.RunMeEvery3MinsBusta'


To find schedule_id, please use below script:

select * from msdb..sysjobschedules where job_id = '533FB186-72E9-40C5-AF88-C8E57F097126'


Here job_id is taken from previous script of table sysjobs.

I have specified this job to run at 2:45AM on daily basis, you may specify other options too.

EXEC msdb.dbo.sp_attach_schedule @job_id=N'533fb186-72e9-40c5-af88-c8e57f097126',@schedule_id=16
GO
USE [msdb]
GO
EXEC msdb.dbo.sp_update_schedule @schedule_id=16, 
        @freq_type=8, 
        @freq_interval=64, 
        @freq_recurrence_factor=1, 
        @active_start_time=153000
GO


Above script is to change job type to weekly, running at 3:30PM on Saturdays.

Hope above helps.