Hello Adytt,
My advise is to simply switch away from ATS as the owner is not much caring about the security or the future of the script, some alternatives you could try are the following.
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https://myarcadeplugin.com/ (base free wordpress required, still being supported and patched, future development expected)
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https://www.avscripts.net/avarcade (no major future releases but is still being security patched and updated)
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https://thebestarcadescript.com/ (actively supported, future development expected, still being updated and patched)
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http://freearcadescript.net/ (support is active, arcade script is free to use, still being updated and patched?)
You could also just do something completely custom and have it secure from the top down.
I hope these alternatives serve you well dude as for working on improving ATS, I wouldn't recommend it since it already has exploits and security flaws which are out there in the public eye.
Regards,
Antz