So my tourneo failed because it needs we long, surprise surprise

After I've welded it am I allowed to used seam sealer and paint the weld and panel to protect them? I understand they might want to check the welds but I can leave it untreated for days on end and it's gonna be a good few days before it goes back in
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You can cover it, you may get advisory repair covered in underseal, espifthey think you are trying to hide a poor repair,
You could always take some pics prior to covering to show the tester,

 

light coat of spray paint over it in the meantime, or protective wax.

No sense putting anything too heavy over it in case they do cry, they need to see it's fully seam welded etc