Not in the Data Manager afaik. But I haven't used it a lot yet. Perhaps it's possible to add a WHERE clause when selecting the data source.
In the Date load Editor you can add a line directly above the load statement to limit the number of records that will be loaded:
LOAD A, B, C FROM ...;
If you use Debug Mode you can also use the Limited Load setting to restrict the number of records loaded. See the online help for more information: Debug the data load script ‒ Qlik Sense