From version 1.7.0 there is possibility to faster import a lot of data from Jira. To use this, you need to tick “Read only” checkbox before fetching issues. If you need to process large sets of data for reporting or calculation without the need to update particular issues - this is the best way.
It is read-only mode, so you can’t send changes made in Excel to Jira on this sheet.
When fetching data from Jira, results are limited to 100 000 issues in this mode.
Tip: Remember you can open a new worksheet and using JQL find issues which you are interested in editing eg, by simple JQL referring to specific issue keys: issue in (key-1, key-2)