this is not possible via UI. I also checked whether this is possible via REST, but it's not.
Only way to do so, is through manually modifying the files and change parameters/values via CLI. But this is a non-tested/non-supported action. Means, you can do this, but if you destroy all, it is not supported.
If you want, you could provide me a backup file of your MWG via PM or create a SR and tell me the number that I can takeover the ownership where we can further communicate. I try to get this modified and send you back the updated backup which you can import on a test machine first for verifying/testing purpose (as mentioned, this is not supported, so only best effort solution). I cannot promise that I can do this but I can at least have a look and try it out and if it works its fine.
Regards, Marcel Kutrieba Technical Support Engineer
Unfortunately we do not have a test machine and we prefer to avoid tests that would impact thousands of users. The best and safest thing for us, even if it will not be the fastest, is to edit manually every single list via GUI