I am planning to enhance erpnext with more apps please advise what will happen to my customization after i do upgradation
If you’ve created a separate app, you won’t lose anything from that app when you upgrade.
If you have made modifications to ERPNext or Frappe code, when you update those changes could be overwritten (but you should get a warning first telling you it can’t merge files). That will depend on whether or not you modified files that are being updated or not.
Ideally you should never directly change the ERPNext or Frappe code, and instead try to implement the changes you want through Custom Scripts/Fields/Forms and a separate app (for server side functionality).
thank you Ben