assign several unique ids per form submitted based on a field value

Unfortunately, this is not possible. A workaround would be to use our Random Value Generator widget (http://widgets.jotform.com/widget/random_value_generator) and add this widget as many as you want to base on the field value. If you allow up to 5 selections, add 5 of this widget.

Here's an example form: https://form.jotform.com/53414059399968.

Using our conditional logic, show how many widgets based on the number input.

http://www.jotform.com/help/316-How-to-show-or-hide-a-field-in-the-form-based-on-the-other-field-input-or-selection

Here's how to add a widget in the form: http://www.jotform.com/help/252-How-to-Add-a-Widget-to-your-Form.

Please do not hesitate to get back to us if you need further assistance.