While waiting for Roon to respond/follow up, I thought it’d be nice to try and find a better answer to this question.
It turns out, that there doesn’t seem to be a free application, specific for this purpose, or at least user-friendly.
It’s sad that I’m so bad with writing software…because the mathematical operations are really not hard.
Anyway. The easiest way to to this, by quite far, is with JRiver. Sorry to mention that name here… I happen to have an old license, and use it solely for audio conversions.
Took an album 44.1khz/16bit FLAC. One hour length. It took a little less than one minute, to flip its phase.
This was very simple to do (first trial took, I guess, about 10 clicks. After which it is fully setup for all following conversions, requiring maybe 3 or 4 clicks).
This time included all unpacking to wav, and recompressing to FLAC (all happening under-the-hood, without user interaction).
You can queue up a few hundreds of albums. Meaning : a few seconds of work. Then go to sleep, wake up, and find your albums all new-and-improved.
Alternatively, it is indeed possible to batch-process them in Audacity. This application is quite a bit slower with the processing.
I think you will run into problems with the more ‘exotic’ formats like DSD though.
And I certainly wouldn’t call it a user-friendly process. (Can explain if appreciated, but wouldn’t really recommend for people that need a how-to…).