Limit characters in getResources parameters

Is there a way anyone has found to limit the number of characters that are shown in the results from getResources? I have it working to show my blog posts and the beginning of the content, but I only want it to show the first 300 characters or so, as a preview. Is there a way to do that?

Have you tried the Ellipsis Output Modifier?

Use this in your getResoures template: