@frob ,
If you want to temporarily remove a SharePoint online site from eDiscovery hold, you can close the case first then edit this case to remove site url.
In retention policy, you can directly edit it or disable it first, then edit site url.
Lastly, you can re-enable them as shown below:
Note:After the hold is turned off, a 30-day grace period (called a delay hold) is applied to content locations that were on hold.
This helps prevent content from being immediately deleted and gives admins an opportunity to search for or recover content that will be permanently deleted after the delay hold period expires.
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