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Save the file as XCF to retain all the original texture colours so it is easier to make later edits.
Checking for 0 and 255 Values
Note before you finish you might want to remove any values which are 0 or 255 (completely black or white) since these can be vantablack (ie no shiny/nice stuff) or highly transparent/shiny (totally alpha/no colour). This texture didn't have that so no need to do it here.
Exporting to PLT
Export As... and select PLT, this has no real options and will just generate the PLT based off the layer names.
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