SUNFISH, that is working under supervision, and your scenario fulfils that definition.
Is a different matter if an unlicenced person fits the propellor without direct supervision.
In fact I have been "pinged" for something similar, wasn't in the vicinity of the work being done.
A more complex issue is sheet metal work
In large MROs the sheeties complete the job, sometimes in stages, and is then inspected and certified by LAME. In a small organisation CASA say that the LAME has to be there on the job all the time the sheetie is working.
Am still arguing that one with them.