The ldappl3.ini file is defined to contain inventory data and allow inventory service to write data into LANDesk DB. So its structure and grouping is hard coded. I don't think you can create a custom subfolder under software inventory.
The point is "why you need a subfolder to contain oacjaged softwares in ldappl3.ini file?" Do you want to open ldappl3.ini file on each client machine to check what packaged software this machine has?
LANDesk SLM or query function can provide you the result that what packaged software is on which machine. I'd recommand you use SLM or query function to get what you need.
Thanks for your answer, but i don't have the time to setup the SLM tool.
Basically I'm building packages for a customer with LDMS but no LANDesk admin, that's why i'm trying to do that with flags or another packaging way.