There is no universal method for converting program written for ISAM 1.x to use ISAM-A, although in general, the conversion is fairly easy, and almost certainly presents an opportunity to simplify your code. From a logical standpoint, essentially all you have to do is get rid of all your extraneous locking and index maintenance operations that are simply unnecessary with ISAM-A.

As a suggestion, it might be good to proceed by creating a set of template routines (open file, find a record, get next record, etc.) for both ISAM 1.x and ISAM-A access. Next, create a simple utility to replicate your template routines into file-specific versions (e.g. open CUST file, file CUST record, get next CUST, etc.) Then replace your embedded statements referencing ISAM statement with calls to your generic routines and confirm that the programs continue to work as before. Then you can start converting individual files from ISAM to ISAM-A by just substituting the template routines for ISAM with those for ISAM-A.