Welding Tips and Tricks

For the autobody repairs that I'm doing, I'm using a lot of mig plug welds. Obviously, these don't have the same appearance as the factory spot welds. I recently picked up an HTP spot welder and was wondering if I could go back and use the spot welder over the plug weld. I've tested it on pieces and it looks OK and seems strong enough. Intuitively, it seems like it should be OK. I'm just an amateur, so I thought I would get opinions from people with more experience. My real concern is does it weaken the original plug weld? Is there any downside to doing this? Any other comments or thoughts?

The spot welder should not affect the weld integrity at all. The trick, I would think, is to reduce the plug-weld with a grinder, without leaving evidence, to a level that the resistance weld will look natural.

Steve S