When TPX is used to access applications across multiple VTAM systems, it is possible that the same applid may be defined in more than one VTAM. So the application would have a different netid, but the same applid.
The TPX ACT (Application Characteristics Table) only allows specifying the applid not the netid.
There is no way to define this 'directly' within TPX (same applid for two different netids).
You may use the 'alias translation table' in VTAM and then specify this alias for the applid within the ACT.