Do you mean using keyword filtering for all feed sources, not individual feed sources?
If so, then yes. In your admin, navigate to the plugin’s settings at WP RSS Aggregator > Settings > Keyword Filtering.
There you have the same options that you have for individual feed sources, only the settings here count for all the feed sources you have.
For example, if you filter in these settings to import feed items that contain the word “bread”, this filtering will apply to all feed items, regardless of their feed source.
Note that if you have any filtering set on individual feed sources, both the global filtering and the individual filtering will work. The individual filtering does not remove the global filtering.
Hope this helps!