As long as it doesn't look like the skin has been thinned at the location of the dent, I don't think the skin needs to be replaced.
I am a huge proponent of the swivel head rivet set and have recommended it for years.
It can be especially valuable to rooky builders for avoiding damage to skins. This comes in handy when less experience help has to be used for two person riveting. Then the less experienced help can be put of the rivet gun rather than the bucking bar, were a mistake can cause major damage.
The swivel rivet set works just as well riveting solo as any other flush rivet set. The rubber cup provides enough friction to keep the set from walking as long as you don't get the gun severely misaligned.
To work well they do require a small modification..... the rubber on the edge of the cup (where it contacts the skin) is too stiff which requires a lot of pressure to keep the set flush to the skin. The edge of the rubber needs to be chamfered at 45 degrees, enough to reduce the thickness to about 50%. Then the swivel set works great.
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Van's Aircraft Engineering Prototype Shop Manager
RV-6A (aka "Junkyard Special ")