Any plugins for "variables" made yet? I'm a bit out of my depth

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Hello,

After moving onto a CDN, I notice a few restrictions with the "replacement variable" feature.
I'm a little out of my depth with knowledge on this feature so I was wondering if anyone could fill me in....

I was wondering is there a plugin (or edit) to let replacement variables only work for certain forums? (I was even considering developing it myself)

Any thoughts or links etc would be helpful. I've looked around but nothing seems to hit the nail on the head.

Thanks,
G