feature request: Substitute log file

It would be great to open a new log file while keeping the same plots open. You can do it now by saving the plots as a custom preset. But I didn't find any way to change the log file without reloading the page.

Start by tracing the current log-file loading flow and the custom-preset behavior described in the issue. Determine how a replacement log can preserve the currently open plots, then verify that changing logs works without reloading the page and that existing preset behavior remains intact.

Written by the indexing model from the issue text.