Been lurking around and found this post. It's a good idea but there is 2 big issues.
1) What is preventing me from taking a stripe of paper with some expose tape in the end, slip it in the flap and pulling out the folded part? The security tape can be finger held down by the opening to prevent it from tearing. I just tried it on a test paper and it worked as the whole flap came out.
You can solve this by getting something like double sided security tape for the 2nd fold but then it'll add to the cost.
2) The worse enemy of all stickers ... good old heat gun / blow dryer
The adhesive will just peel off if you work at it long enough. Unless there is some heat sensitive ones I am not aware of. Even so that will add to the cost.
Low tech solution to a high tech problem

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