In Mass Hunter and the old Chem station you can edit EPA.MAC to change significant figures in the sample report.
How do you do this in Open Lab using Classic reports?
You are going to need to be more specific. Which OpenLab product are you referring to? Both OpenLab ChemStation and OpenLab EZChrom have reports referred to as "classic reports" in the application. It would also be helpful to know what revision of software you are running. This can be determined by going to Help>About.
How is this, Open Lab CDS Chem station C.01.07 
Setting the number of digits after the decimal that a classic report template reports for a given field is not as straightforward as just editing a .mac in notepad. It involves editing the .frp report template in the ChemStation application and then saving it as a new custom report.
The first step is going to be disabling Intelligent Reporting in the instrument configuration which will then allow us to access the older Report Editor from the A and B revisions of ChemStation. To do so you need to close all ChemStation instances running on your PC and then right-click on the instrument in the OpenLab Control Panel and select the option to Configure Instrument. In the Configure Instrument window, you then want to uncheck the "Enable Intelligent Reporting" checkbox under Options:
After making this change, when you access the Report Layout view of OpenLab ChemStation for this instrument you will now be able to load and edit .frp report templates as opposed to the Intelligent Reporting .rdl templates. To load a template just go to File>Open Template and select the appropriate .frp file. As an example, I have loaded the areapct.frp template which corresponds to the Area Percent classic report
Now to edit the report in order to change the number of places after the decimal a value is reported out to, you need to select the relevant report item on the template by left-clicking it. Then go to Edit>Setup Element. If this is a table that you are editing, you will then have the ability to select which columns to include in the table. Then if you click on the 'Edit Format' button, you can now edit the Precision value for all of the table columns which control the number of places after the decimal each column is report out to:
After making the change to the column precision, click OK. Now you need to save the report as a new template by going to File>Save Template As. Once it is saved, you will need to add the new template as available Report Style that you can select from in the Report Layout section of your method. To do this go to File>Add to Report Styles and then specify the display name for the template's report style and click 'OK':
You should now be able to select the Report Style in your method if you go to the Data Analysis view and select Report>Specify Report:
For this example I had changed the precision of the response column in the results table on the area percent report from 3 to 5. Below you can see that my new Community report template is now reporting out the Area to 5 places after the decimal:
Hopefully this helps.
Retrieving data ...