PA_ORG_CLIENT_EXTN Change Organization on a Project

Hello,

Customer is using PA_ORG_CLIENT_EXTN to determine whether an organization change is allowed for a Project/Task Owning Organization, and to define the error messages that are used when the rules are violated. He says that the message shown is different when changing Organization in Web (Project Super User > Search Project) Project Setup and in Form (Project Costing Super User > Projects).
His questions:
1. Is PA_ORG_CLIENT_EXTN performed for Web only?
2. What’s the API performed when changing Organization in Form (Project Costing Super User > Projects)?

Customer product version = 12.1.1

Please advise.

Thank you,
Cristina