Can someone add or remove anything from my luggage?

No - all bags are sealed in Tamper Aware Bags or using Tamper Aware Seals upon collection and remain sealed until they are handed over to your airline for your flight, at which point the TAB's are removed, but TAS's remain on your bags until they reach the destination airport.

All baggage handlers are subject to strict interview processes and criminal background checks. Vehicles also remain locked at all times when in service.