If you have a proxy in place the best path forward would be to make this customization via the proxy server you're using due to the fact that the changes in BitBucket itself will revert after an upgrade, etc. Here are some resources you can use to create error pages in the environment you're using as a Proxy:
Hello! My name is Mark Askew and I am a Premier Support Engineer for products Bitbucket Server/Data Center, Fisheye & Crucible. Today, I want to bring the discussion that Jennifer, Matt, and ...
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