I'm wondering if I should have said anything.
The short answer is 'yes,' you can append lines to the end of the PLC without having the source file.
Here's the problem(s): You need to either be able to edit the PLC from the front panel, or be able to download the object file, disassemble it to commands and addresses, insert the two lines you need just before the EOP, and re-assemble to machine code, then upload back to the control. Unfortunately, not many PLC could be edited from the front panel - that came very late in the product life. I think it would have to be a Delta 40/50/60, but I'm not sure.
My problem is that it's been 9 years since, I've worked with a DynaPath or even in the machine tool industry.
Frankly, you've got a method that works and I don't think you should mess around too much trying to edit the PLC. The editing process was flaky and unreliable. I don't want to be the one who leads you down a path of screwing up your machine.
Best regards,
jagardner4