Yes, you can use an app_config.xml file, documented in the User Manual

The tasks that use all cores are called Multi Threaded tasks: the example given in the manual covers that case.

You have to identify exactly which project and application version is associated with these tasks: it's possible that the project's own website has a discussion of the problem and example files. Then, fill in the lines for both <avg_ncpus> and <cmdline>--nthreads with the number of cores you wish to use.