Again, to be clear, regardless of whatever build you do or do not use backwards compatibility is something we, in general, try to guarantee, and such breakages are bugs which we try to fix. As far as 'SCP Policy' goes that hasn't changed.
In that thread, I didn't entirely understand the situation he was in, and I recognize now simply sticking to an old build is probably not a workable solution. Mods under active development almost always needs to be on recent builds, as they typically request and then rely on new features. Unfortunately, especially in the case of large mods with multiple campaigns developed over many years like BtA or BP, this can 'drag' older campaigns or missions which used to work under the purview of new builds and break them. While this is a great way to discover bugs to fix, it's understandably frustrating for the modder. Mods like these simply have a large 'attack surface', they are complex, rely on many different features, and there's a lot of content, all of which adds up to a high likelihood that something gets broken along the way. There's no real fundamental solution to this I know of, as long as new features are added the risk of new bugs is ever-present.
In any case, the SCP's 'answer' to any bug or breakage of backwards compatibility is the same: a bugfix. (Exempting some extreme circumstances, I'm sure there have been or will be extraordinary scenarios I haven't thought of where the bug was simply too hard to fix, or the breakage was worth it or something)