This hack will allow you to enable and disable the qucik reply on a forum per forum basis. After you install it, go to your Acp->Forums & Moderators->Forum Manager. Chose the forum where you want to disable the quick reply, click at Edit Forum and all the way to the bottom, under Enable / Disable Features, you will see a new setting that says: Disable Quick Reply, set that to yes.
For more information, please have a look at the attached screenshot below.
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