Quality being involved tells me that winglit's tech services people aren't design approved. Ordinarily a designated TSE will draft a repair scheme under the airline or MRO's company design approval. The LAE will then carry out the approved repair and certify it in the same way as if they were doing an SB. The paper chase leaves an audit trail and QA's involvement is restricted to auditing organisational compliance with procedures and practices, not individual repairs and modifications.
ASKAP's question: Why do an approved repair when the job is within SWPM (or SRM for structural repairs) limits?
You don't legally need to as you will have satisfied the airworthiness requirement. Lease return conditions are, as winglit says, another matter. The lease contract will usually specify FAA certification for all repairs although EASA is often accepted these days. So, if you certify all repairs with an FAA 8110-3, the leasing surveyor can argue all he likes about it, that's an "as new" condition. When you buy a brand new aeroplane the delivery docs will be full of variations and production line repair data; There's no such thing as a perfect airframe.
If you repair engine wiring on wing, repairs given in the SWPM repairs are derived from the airframe manufacturers drawings and the audit trail will lead right back to the Type Certificate Data Sheets. A spare engine on a stand in storage is a different matter and the engine manual is the reference document.