Load Defaults, Allow Modification

My form confirms components for a product prior to assembly. Each field is pre-loaded from the spec for that product. Occasionally, the user overrides the spec with a known item or custom item.

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Question:

Does my design have any obvious flaws? If so, please describe.

Notes:

• The Value initializes from the spec.
• The last Value is (Custom) to require a Custom entry. The user must actively look through the list before resorting to a Custom value.
• A highlighted row indicates the property has been overridden.

Also considered:

• Displaying SpecValue - for reference without resetting
• Editable dropdown - more compact

P.S. I have no formal design training, and I tend to overthink design, getting stuck not knowing what is best.