[Sylontack]

Obligatory "clearly made an account just to ask this one question because I'm in over my damn head" post here. Forgive the size, I'm super wordy and I've been trying to sort this out for quite some time so I've a lot of talk piled up in my brain on the matter.

So I've used MultiAVCHD a couple of times to add audio and subtitle tracks to BDMVs and it's mostly worked out pretty well after some trial and error.
My next few intended projects are TV Series BDs instead of movies and those ones are a bit more complex authoring-wise for me. So I understand from the first page which I've gone over lots of times over the last year or so on various projects that series and multiple cuts are harder to work with, and the tutorial doesn't actually apply to the way the discs I'm working with are authored (neither have individual playlists for each episode for example). I've come to the conclusion that the most painless way to achieve what I'm after is to just mux the new audio and subtitle tracks into each m2ts stream file and replace the originals.

Of course I'm also aware that just muxing the new stuff in will result in a disc that won't play. I know that I need to work with the IN and OUT times in some way but I've never found a good explanation of how those work that made any sense to me (I've seen lots of people just say what to do with them, but if I don't understand what they are or how they work I can't adapt it to my project).

Basically to disregard all this context I've given; is there a simple and painless way to just completely replace the video streams with almost identical files while still keeping the disc otherwise unchanged? Alternatively is there a way to use MultiAVCHD to add streams to the video files themselves rather than the playlists? As some of my discs only have the master playlist with all episodes at once, and some have multiple playlists for one episode (despite only having one m2ts file for the episode), I fear it'll be too complicated to work off the playlists.
I'd also be interested in editing the menu to read in English and add options for my new audio/subs but I fear that'll get way too messy so I'm not very fussed about that.

So if anyone here is familiar with achieving what I want (basically anyone who works with Anime series BDs will probably know exactly what my issues are), any help would be seriously appreciated. I've been trying to get this going for quite some time now and I've given up on trying to learn on my own.