For you specific questions:
1. You could disable the Auto-update definition under the Tools menu. This will prevent the definitions from updating before scans are run.
2. You would need to ensure you don't have Scheduled Automatic Downloads for Core engines/definitions in Tools > Options > Downloads.
3. You should also make sure no one clicks on Help > Refresh Files. (there is no way to disable this button)
An alternate better method:
The only method I would use is a Patch Group. It's the only method to be 100% sure you are not including patches outside of what is included in the group. An helpful customer shared a PowerShell script that uses a SQL query I provided and utilizes the API feature in Patch for Windows Servers to create\update Patch Groups with patches released between 2 dates. This includes some product filtering that is completely optional.
This is the thread: Re: API / Powershell to update Baseline
Link to the SQL query that will output a list of QNumbers released between 2 dates: https://community.shavlik.com/servlet/JiveServlet/download/2254825-3017/PatchesBtReleaseDateTimesRange.zip
This is a direct link to the PowerShell from the customer (this can be used as an example) : https://community.shavlik.com/servlet/JiveServlet/download/2254841-3026/Ivanti_Update_Baseline.zip
Let me know if you have any questions,