I had a Sunline trailer with aluminum siding that ended up having some decals that needed to be removed. I found WD 40 to be pretty good at helping remove the decals and adhesive residue. I used a hair dryer as a heat gun and plastic putty knives. After removing the decals (white siding), there was some difference in the color so you could see where the decal was, but it wasn't anything that I worried about.
Since I didn't remove all of the decals, I didn't even consider replacing them. With a ten year old trailer, I wouldn't bother trying to replace the decals. But you could consider adding some after market pin striping or whatever is available that would be easier to install on the siding. Or, if you have the skills, spray paint your own striping/design.