Select override value (or type manually)

My form should confirm the components for a product prior to assembly. Each field would be pre-loaded from the specification for that product.

Occasionally, an override of components is approved (R&D testing, ran out of a component, etc). A dropdown would list alternate components in the database. If not in the database (ie: R&D single use), the user would type out the component used.

Planned interface for each field. Grid of:

{FieldName}, [{DatabaseValues}|v], [TextBox], {ResetLink}

• The DatabaseValues dropdown would have SpecValue selected.
• The last item of DatabaseValues would be (Other...), and selecting it would enable (and require) a TextBox entry. The intention is that the user actively looked through the list before resorting to the TextBox rather than just typing in an editable dropdown.
• If SelectedItem != SpecValue, the row would be highlighted to indicate the override.

Also considered:

• Override checkbox - more explicit, I save it anyway for highlighting
• Separate label for SpecValue - for reference without resetting
• Editable dropdown - more compact

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

Question:

What "design rules" (if any) does my planned interface break? Please describe why any improvements would be "better" than what I have now.