EDIT

Can you please test all possible combinations on nightly and put the result of the test into this ticket?

Tested locally (test server is unavailable):
pref: keepOrWarn

• if the secs the same -> ok
• if secs different -> warning, but secs kept

pref: keepOrSelect

• secs are all the same -> ok
• secs are different -> dialog to choose how to handle the sec

pref: always select

• secs are the same -> dialog
• secs are different -> dialog

pref: always delete sec

• sec of the moved taxon is always removed

pref: always use parent sec

• sec are the same -> sec is kept
• secs are different -> moved taxon gets sec of the parent