What lies under the hood of design and development

Answer
I must confess that before reading your question at the end I was already thinking about how strange: a company is dealing with personalized solutions being exempt of design and development.

The process for design and development is how your company design a develop a new solution fo r a customer:
First you have to consider the inputs: client requirements; legal and regulatory requirements; your own manufacturing requirements; your expertise and past experience requirements. This will help your design and development team decide if and when is the project terminated (what is called verification activities in ISO 9001:2015 – to check if the output of the project is according to the inputs);
Then you have to develop the project activities to turn inputs into outputs (for example, choosing materials, choosing software, making prototypes and test them – those tests are what is called review activities in ISO 9001:2015)
After a successful verification it is wise to get client approval, for example after simulation tests (those tests are what is called validation activities in ISO 9001:2015)
A successful design and development do not end with a validated output. It also answers to questions like: What are the specifications of the output (product and/or service)? What are the specifications for process and quality control during production? What are the specifications for buying raw materials or subcontracting? What are the requirements for monitoring resources? (This is what ISO 9001:2015 calls design and development outputs)
Once your company develops the previous activities in a planned and systematic way, to meet deadlines, to focus design and development team’s attention it is useful to start each project with a plan. (This is what ISO 9001:2015 calls design and development planning)
The client validated the product and production started. Changes always happen, because of a complaint, because of a change of materials or suppliers, because of a change of production process. Changes must be treated, tested, validated and documentation and practices altered in a controlled way to avoid chaos. (This is what ISO 9001:2015 calls design and development changes)

The following material will provide you more information about design and development:
The ISO 9001 Design Process Explained - https://advisera.com/9001academy/blog/2013/11/05/iso-9001-design-process-explained/
ISO 9001 document template: Procedure for Design and Development - https://advisera.com/9001academy/documentation/procedure-design-development/
- Free webinar on demand (you can see here information about non-applicable clauses- ISO 9001:2015 clause 4 - Context of the organization, interested parties, and scope - https://advisera.com/9001academy/webinar/iso-90012015-clause-4-context-of-the-organization-interested-parties-and-scope-free-webinar-on-demand/
- Enroll for free course - ISO 9001:2015 Foundations Course - https://advisera.com/training/iso-9001-foundations-course/
- book – Discover ISO 9001:2015 Through Practical Examples – https://advisera.com/books/discover-iso-9001-2015-through-practical-examples/