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You could use the regular expressions filters to do that. But first, you need to invert the question in your head to make more sense in this context. You want to find out how to exclude all tables EXCEPT FOR the few tables you want to back up. Assuming that the tables start with #__community (remember that #__ is how the table name prefix is denoted internally in Joomla, therefore in Akeeba Backup as well) you need something like

!/^#__community_/

The exclamation mark means "invert this rule". The slashes are the delimiters inside of which we place the rule. The caret means "starting with". Therefore this rules means "every table whose name does not satisfy the criterion ‘begins with #__community_’". There you have it :)

For what it's worth, an example similar to this can be found in the documentation.

I hope this helps!