Hi,
As explained in docs
Unloadable:
Select the check box to create Customer Update [sys_update_xml] records when the fix script runs. Clear the check box to run upgrades without creating these records (default). Unloadable is enforced when you test the fix script.
This means it will not create entry for update set table. There are lots of table having update_sync attribute and their entry goes to update sets but if you want to do such task from fix script then you have an option to avoid them to capture updates.
Run once:
Run once Select the check box to run the script only one time (default). The fix script is ignored for subsequent upgrades.
Clear the check box allow the script to run every time the application is installed or upgraded.
It means it will be running only once if you still have confusion see example mentioned in point 2 of below link.
https://developer.servicenow.com/app.do#!/document/content/app_store_doc_parts_of_application_jakarta_t_TestFixScripts?v=jakarta
Hope this helps.
Regards
Ujjwal
