Is there a way for one program to open and close files and from other programs in the same run perform all the updates (read, write, re-write, delete) to the file?
Yes this is possible if the file FD is declared as external in both programs, ex:
FD custom-file external.
01 custom-record ....etc
This way it is possible to open and close the file in one program and read, write, etc. from another program.