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Regarding 2): that makes no difference. The idea for a bot is to look for a certain pattern in a string and do something in case it finds it. Since the text would have to contain what the code is for (otherwise humans don't know what it's for) this is easy. The "harder" part is to extract the code as it usually requires knowledge about regular expressions, which the majority of coders have (the rest googles for that).

To make that harder the code can be shown as an image (similar to Recaptchas) made available with a link as you can't show images in the chat directly. However, then the codes need to be simpler to avoid typing errors and such.

Then the code could consist of UTF-characters outside of the regular ASCII-character set. There are character that look exactly alike. However, it's also easy to code a mapping to convert them.

Something else could be a simple math calculation where the result is the code. If you use Mindark's website to write support cases you should know what I mean. It's also easy to code something for that.

Another idea is that Tia's chatbot logs activity of the users in that channel and uses that info when users post the code. That has to stop logging before the code is posted, otherwise everybody posts like "whow" into the chat after the code appears and may use the code.

Quite something to think about if this is supposed to be done right... Will it be perfect? I doubt it as the coders who want to achieve something usually are ahead of what the service should protect.