Changing Shopping Mode - from Confirmation to Product Page

[PA.com]

Hello, just looking for advice if possible please.

For all of my website's Actinic 7/Sellerdeck life I have used the Shopping Mode 'Quantity on Confirmation Page'. Can't quite remember why I set it up like this, as the quantity for all of my products must be 1, but it must have seemed like the better option at the time.

Now I am looking to switch to 'Quantity on Product Page' site-wide and would like to know which scripts this changes please (and how), so I know what to refer to should it all go wrong.

I remember trying to switch it for a single product at Section level once (in Page Settings), and the website threw up a nasty error message when I tried to add this product to cart. Any ideas why this would be?

Thanks in advance for any help.

[PA.com]

In case it helps anyone in future, I was able to solve what was going wrong here. Some of the <form> </form> elements of my product pages and inner section body pages had got out of sync, which is why when I tried switching to Confirmation on Product Page it would throw up an error message on the website. Also I had commented out some of the Quantity elements within the product pages and it turns out these were necessary to reinstate. In terms of scripts I’m not altogether sure what if anything changed on site in terms of Perl, but I did notice a .fil file was altered in the procedure.