Hi!
Well, that is not possible to change unfortunately. The limit is hard-coded as the number of results to load per batch. Maybe changing the limit to a smaller number, like 50, so that there is still many loaded, but the next batch also comes up with 50 results.
Appending something to the end of the list at reaching a certain number of results might actually be possible with a custom script. I have constructed a custom code that appends a paragraph into the results box when a certain number of results are reached. Add this custom code to the functions.php in your theme/child theme directory (copy from line 3 only!). Before editing, please make sure to have a full site back-up just in case!
Change the text, search_id and the results_num variables according to your needs.
Please note, that this may not work in all cases, as it is a customization.
You can style the text by adding rules to the .extra-text CSS class:
[html]p.extra-text {
}[/html]
I hope this helps!