Can the ALWNULL(*USRCTL) option be limited to a specific file?

I have a vendor provided program as part of their package. We have
modified it to include information from one of our home grown files. Our
file utilizes null fields. I'm now merging our changes with the most
recent vendor release. That and we're now on version 7.1 (coming from
V5R4). So I don't know if my problem is a vendor change or an OS change.
The problem is when I run the program, I'm getting a CPF417A escape
message ("Handling null capable fields is not valid for open of member
xxxxxxxx.")

Member xxxxxxxx is not the file with null fields. I'm still researching,
but it appears a shared open is done on the file earlier in the job
stream. Now when the program in question is called, it receives the above
error because the earlier open was not coded for null fields. (Changing
all the programs to include ALWNULL(*USRCTL) is not a realistic option.)

Earlier in the job stream, the vendor does an override (with SHARE(*YES))
in a CL. The OVRDBF does not specify the activation group. Since the
default for OVRSCOPE is *ACTGPDFN and the CL runs in the QILE activation
group, I thought moving this customized program to a different activation
group would solve the issue, but it doesn't.

Is there any way I can limit the effect of the ALWNULL(*USRCTL) to only
the file that needs it? Or are there better techniques to handle this?

Thanks,
Michael Quigley
Computer Services
The Way International
www.TheWay.org