There is a product called Undu that will temporarily deactivate the adhesive on the decal, and leave it so that you can reapply it later.
I've never tried it on a project that big though.
The problem you would have though is keeping the decal from stretching while you remove it.
You might hit up your local sign shop for an almost empty roll of application tape, put that over the decal, and THEN try using Undu on it.
The other downside is that Undu smells like skunk (literally!).
If you use enough of it to remove those decals, be sure to do it in a REALLY, REALLY well ventilated area.