Short notice to this problem. It is no real problem with 1.6 to keep the “modified” tag group.
The problem will be only then later with the 2.0 upgrade.
My procedure to clean up this problem was the following.
First remove all modifications like the first picture from @tosch it shows.
Second step is the same as the picture “Hosts before deletion” shows, inspect the tags on the normal hosts.
SNMP hosts should have the tags - snmp:snmp - snmp_ds:snmp-v2 or v1 and agent:no-agent
Normal agent hosts should have - agent:cmk-agent, tcp:tcp, snmp_ds:no-snmp
All this is done after the upgrade to 1.6
I don’t try to delete the tag groups is WATO - i had only problems with this way.
Instead i edit the file ~/etc/check_mk/multisite.d/wato/tags.mk
Only solution there is to remove the tag group from the file. It’s a nice dictionary.