I Accidentally Allowed External Apps to be Used. Is there any way to reverse this? ?

This is what I got
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An external application is needed to handle:

file.pdf

NOTE: External applications are NOT Tor safe by default and can unmask you!

If this file is untrusted, you should either save it to view while offline or in a VM,
or consider using a transparent Tor proxy like Tails LiveCD or torsocks.
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This above warning no longer exists whenever I click on links that used to show the above message. Is there any way where I can make that warning message reappear whenever I try to open links that require external applications? That's all I am asking

 

Did you click "Do not show again" perhaps? By the way, unless you're actually letting the file run, be it a .pdf file in Adobe or a video file in say VLC player, instead of just saving the file to the disk to run later, you're not in danger. It's only if, say, you choose "open file with *program name* instead of saving the file that puts you at risk of being "discovered".