As you may already know you can add custom data to Workfront items (project/task/issue/user, etc.) via Kickstarts import. Please, note there is no option to edit existing custom data via Kickstarts you can only add new custom data. In case of adding certain option for your multi-select custom fields (like radio buttons, checkboxes) you should use custom data delimiter "\|" to separate the values of these options in the Kickstarts template.
Let's take a scenario where we need to add the options "A" and "D" of our custom checkbox field named "Departments" nested in a task type custom form "Additional Task Details" to a Task.
Here are the steps to follow to add these options:
1. first you need to download a Task template from Setup>System>Kickstarts>Import Data;
2. after downloading the template open it up and you will see the "Preferences" sheet where the symbols "\|" are set as default value for custom data delimiter:
3. now navigate to the main sheet "TASK Task", fill out the all required fields for your task including the ID of the above mentioned custom form "Additional Task Details" under the column "setCategoryID";
4. before filling out the options of the Checkbox type custom field you first need to add a column for the field itself with the appropriate field name. Please, note for the all custom fields you should add "DE:" in front of the name of the custom field. So in case of "Departments" field you should name the column as DE:Departments;
5. you have finally reached the step for applying the delimiter. Under the "DE:Departments" column on the row of the task you want to attach the custom data to you should type in A\|D. Please, note there is no space between the delimiter and the value name:
After saving the file and importing it into Workfront you'll get the following results: