You must first switch groups before removing the last license, in the below example we are using the 'Free' license group.
Via the GUI;
Settings > Licensing > Change license group > Free license (save and 'restart now')
Or via the CLI;
$SPLUNK_HOME/bin/splunk edit licenser-groups Free -is_active 1
$SPLUNK_HOME/bin/splunk restart
Once splunkd restarts, re-run the license removal operation, first running 'list licenses' to confirm the correct hash for the license to be removed;
$SPLUNK_HOME/bin/splunk list licenses
$SPLUNK_HOME/bin/splunk remove licenses <hash>
Subsequently installing a new license will automatically switch to, and make active, the group appropriate to the type of license installed (Enterprise, DevTest, etc) following a restart of splunkd.
Add the new license using the GUI;
Settings > Licensing > Add license > <select license>
Or add the new license using the CLI;
$SPLUNK_HOME/bin/splunk add licenses <path_to_license>
$SPLUNK_HOME/bin/splunk restart
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