How to protect composite deck boards while staining...

I'm in the process of staining/sealing cedar boards which are attached to composite decking. Unfortunately, while staining part of the deck, some stain seeped through the blue painters tape that I applied over some of the composite. So now I have 2 challenges. First, is anyone aware of a chemical (I've tried lacquer thinner without much success) or some other process to remove stain from the composite? Second, is their a better tape or technique to prevent getting stain on the decking material when the edge to be stained is attached flush to the decking?

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