As you said, the existing action already recorded the 
objects into object repository pertaining to the when you 
call the external action,it will added the objects to the 
existing one

If the calling test uses a per Action Object Repository, 
then:
1. QTP cannot call Actions that use a shared Object 
Repository.

2. QTP can call Actions that use a per Action Object 
Repository, but it will be read-only.

3. QTP can call copy Actions that use a per Action Object 
Repository. 

4. QTP cannot copy Actions that use a shared Object 
Repository.

If the calling test uses a shared Object Repository, then:

1. QTP can call Actions that use the same shared Object 
Repository as the calling test.

2. QTP can call Actions that use per Action Object 
Repositories.
You can instruct the external Action to refer to its own 
Action repository or to use the same shared Object 
Repository as the calling test. You do this in the External 
Action tab of the Action Properties dialog box.

3. QTP can call Actions that use a different shared Object 
Repository than the one used by the calling test.
The called Action will use the calling test's shared Object 
Repository.

4. QTP can copy Actions that use shared or per Action 
Object Repositories.

QTP only copies in the Action, not its corresponding Object 
Repository.