First, you should always have a backup of your site before you install any modification.
Second, if you can at this point, just disable the modification and leave a message for @ozzy about the uninstall procedure -- if it is not included in the download file.
Third, if you have not backed up your site, do so now.
When you have time try to create a local test site and test your modifications there before trying them on your main site, but always back up your main site. (Have I said this enough.

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