The WebAssist interface for changing the JQuery presets is actually a feature of eCart. So you would need to have eCart installed in order to edit them using a UI.
JQuery Validation was added as a feature to eCart, but we updated the rest of the product line to also use JQuery Validation in generated forms. I'm not 100% certain, but I believe the access point and UI will be included in future versions of products that also leverage JQuery Validation.
You can manually edit any preset CSS you apply to your Security Assist pages. It is located in your site at webassist/jq_validation/{preset name}.css