Substitution rule has to triggered after save document in FB70 and FB75

HI,

I have a substitution rule for REFNR field and that will trigger when you make FB70 and FB75 for 2 company codes. In the user exit for subustitution we have a code to get the next object number for some other purpose. because third party will use this generated next number for their legal requirement.

The real problem comes this substitution rule is triggered before save document. due to this if i came back from the transaction without saving the document I am losing that generated number which i dont want.

I need some tips on this. is there a way in the substituion settings we will trigger this exit at save document.

I would appreciate your inputs on this.

Regards

PRasad