You may need to perform export/import process to provide the custom value you would like to use during the provision, mailbox enabling process, etc. such as SearchKey2 value for user/resource migration.
Import members from TSV option on the Manage User Collections section of the tool is taking very long to complete.
STATUS
Enhancement request TFS276562 has been submitted to Development for consideration in a future release of Notes Migrator for Exchange.
WORKAROUND
Use the Import objects from TSV option located on the Export Notes Directory section of the tool.