I've just finished up the option file I'm going to be using for my ML. It's not complete - see below - but the leagues I'll play in are updated. Thought I'd share in-case anyone is waiting for similar.
This file is 99% the work of others - it's based on PESVicioBR v2 (which itself uses the Bundesliga from PES Universe, amongst many others). More info here:
https://pesviciobr.blogspot.com/
In this file, almost every league is updated in some way (even licensed leagues have manager names, stadium names, rivalries etc.) - EXCEPT for "Other European Teams" (about five are still fake), and the fake American/Asian leagues (untouched).
My only additions were to update all manager names, stadium names and rivalries for the Premier League, Championship, La Liga 1&2 and Serie A&B, plus a few other small fixes and changes (such as, in my opinion, better competition logos that don't feature the year/venue of an event).
I've also added Tranmere (to replace the fake Palermo) - entirely optional (and labelled so that you can ignore it if you like) but if you want a challenge akin to starting with the old ML defaults, you'll like it! Recreated using slightly modified FM data. (Thanks to
@xPJRx for the kits, I've modified them slightly to account for the badge on the sleeves amongst other things!)
There is also a manager in the list of managers you get to choose from (Maradona etc.) who looks really similar to Tranmere manager Micky Mellon, so if you choose them, why not select him?

(I can't remember his name, he's an overweight guy with short grey hair and blotchy skin...)
Not sure if the TEDs are in the right place though, that's the thing... I'm about 80% sure...
If you want to give it a go, you can download it below. Instructions - apply the Live Update first (through the PES 2020 system menu), then pay attention to the folder structure so that you know which files to apply with data, and which to untick the data box for upon importing. (The "0. Fix" folder requires importing with data.)
Afterwards you'll need to edit competition structure so that the Bundesliga has 18 teams and so that the right teams are swapped in - and if you want to play as Tranmere, you'll have to swap an English Championship team with Tranmere from the "Other European Teams" (my recommendation is Luton).
I also would not recommend importing the "LEGENDS" directory because, although it imports all myClub legends into the offline game, the original, fake legends are given OVR 40s and released so that they appear in MLs etc. - whereas if you don't import them, you'll never see them interfering with the ML because they stay in the classic teams. But I've left the directory in there if you want to play with the (real, from myClub) classic players!
https://www.mediafire.com/file/gv9ahmzen6t5jx1/Chris's_PESVicioBRv2_Update.zip/file
For a complete file, you just need to import the missing Other European Teams, Liga MX / MLS and J-League, when they're available (PES Universe are working on it).
However, when doing so, you might run out of kit space - I haven't bothered creating stsdium and manager images for the leagues I've updated, because I'd rather try and fit the missing leagues in using a small kit format whenever they arrive... But in all honesty I think, at that point, kits will have to be downsized.