You can use custom JavaScript code in import options "Additional options" tab to modify received issue JSON object before importing issues into flex.bi. Click Add custom JavaScript code to show the code editor.
You can useissue variable to access received Jira REST API issue JSON object properties and modify or add additional properties. Please openJIRA_BASE_URL/rest/api/latest/issue/PPP-NNN?expand=changelogin your browser (where PPP-NNN is issue key) to see sample issue JSON.
Then switch to flex.bi import options and use the"Additional tab"to add custom Javascript code in the code editor [1]. You can test the code for one sample issue key in the validation area[2] and see results in the results pane [3][4]
Here is an example of JavaScript code which will clear issuesummary property for issues with issue type bug