No, it has to fit the naming scheme of an existing index set.
Additionally, you have to recalculate index ranges for the respective index set.
It has to match the configured index prefix of an existing index set (e. g.
graylog_*) and end in a number. So
graylog_400 would actually work (given that there will never be another index named
I would recommend creating a specific index set for these shrunken indices which isn’t used for anything else, so that there won’t be any name collisions.