Eugene,
So sorry to see this. Both Tamiya and Testors/Model Master clears are lacquer based not acrylic based. As Richard said too much to quickly and it will eat right through paint, decals, everything down to the bare plastic. It's what lacquers do.
I've been using Testors Dullcoat and Glosscoat for more then 40 years, tried other brands/types and still went back to them. But I've never applied them with a rattle can, just with a air brush. The problem you had is that the rattle cans put out way to much material, way to fast, and you get a heavy build up which will eat through everything. It can even damage the raw plastic. If you must use a can, then quick lite coats, but give each coat a min of 10-15 min to set up. If you have a air brush, then use it.
As for using Future/Pledge as a barrier coat, with the amount of Matt you applied, it would eat right through it as well.
there is unfortunately no quick easy fix. My guess is that you're going to have to completely strip down the P-51D to raw plastic, fix any plastic issues, the a re-paint and re-decal.
Joel