Hi. COVID sucks, I have a half hour to kill. Here's a small novel.
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Yes. Both. Yes. Sure, skip down / skim, or just read it.
Assuming you extracted the hugin source thusly?
D:\code\hugin\hugin-2019.2.0> grep -RHEn "(_blended_fused|_fused)" *
StitchingExecutor.cpp:697: const wxString fusedExposureLayersFilename(prefix + wxT("_blended_fused.") + opts.outputImageType);
StitchingExecutor.cpp:738: const wxString fusedStacksFilename(prefix + wxT("_fused.") + opts.outputImageType);
Just change the text in the quotes to "_bf" and "_fd" and compile. Doing it this way will change it so any reference by any of the multiple programs that make up hugin will use your truncated names, and nothing will break or require hand-editing to fix. (Note this is not what you should be doing, but that is what you asked for.) You'll need to install a LOT of tools, first of all even grep is not part of Windows by default. There's no unix dev environment by default. You can enable the Windows Subsystem for Linux (WSL) if you want to get that going, but you'll still need a full GNU dev environment and all the prerequisites installed and properly configured.
Don't take this the wrong way, you were trying to hexedit the precompiled binary of an open-source project to change it, so this is might be a long road for you for something simple.
I'd suggest 2 alternatives. 1) Just write a batch file to rename the files after-the-fact, or 2) customize an executor so you can make your own output filenames, that's what most of us do.
Let me outline an example:
Go into Program Files\Hugin\share\hugin\data, pick the one you have the problem with _blended_fused, which is fused_layers.executor. Copy that to something else, abri_fused_layers.executor then edit it. (use something that understands unix line endings like notepad++ / bluefish / brackets / even wordpad) Change the Description= and Help= lines, to make it something unique, now go down to the Result line and change it to read something like Result=%prefix%_bf.tif
That's it. Save and exit. Now load up an already-optimized and ready-to-stitch .pto file in hugin gui, click Output / User defined output sequences / and the Description you chose. Boom, there it goes. And there goes your intermediate files being named what you wanted. You can make as many of these as you need, every scenario every file type, there's enough examples in that directory for you to customize anything you want, and again, no recompiling required. You could make your own assistant if you chose to.
I'm not sure if there's a default one that you can change the executor of that will change the hugin GUI so that when clicking the Stitch! button with fused and blend settings, it'll use your modified version, or if you'll need to recompile for that. But this here will get you going.
Have a great day.