Still curious about the function of that metal/plastic thing, but I solved my modding problem more elegantly...
The access compartment that each fuse is in is deep enough to accommodate another fuse in each.
To insulate, I put the spare fuse inside some 3/16" shrink tubing, which I cut slightly too long for the access compartment so that is wedged in when inserted (no rattling).
See photo (license plate number obscured to foil criminals) showing spare fuse installed on left side. Life is good.
Now as long as the fuse doesn't get so hot when it blows that it heat-shrinks the tubing on my spare, hehe.
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