Query - Custom Business function

Dear All,,

My query is relating to new business function.

Developer created a new custom business function and this is been used by three of the application.

A project contains - data structure, new custom business function, two standard Application in which one is having a version and one custom application.

In PY we build the full package for the new business function and its working fine .

But the question to u is in production these three application is running and if we promote the project to PD the running application will stop working.

Please suggest how to promote these object without impact to current application in PD.