how to properly override the function?

I am working on my first theme. in the tpl_product_info_display.php page, it uses " zen_get_products_display_price((int)$_GET['products_id'])" to display the price.
this function added "<br/>" tag
$35.99 $30.00
Save: 17% off

I want this to be one line. ($35.99 $30.00, Save: 17% off).

I try to add "my-style" folder to "includes/functions", then override the function. but its not working. I prefer not to change the function file directly, please show me the proper way to modify the functions.

Due to the way functions work, there are no overrides for function files.

Hate to bring up an old thread... but is this still the case? If so, is this person's method sound: http://stevenkohlmeyer.com/development/web-development-and-administration/zen-cart-html_output-php-overrides/

FWIW, I've used that function-override method for a couple of years now. You just have to be aware that your 'override' function files will still override (sometimes when they don't want to) on any Zen-Cart version updates you might apply to your installation, but it does serve to highlight which function-related files you've modified.

Good, thank you.