Play a specific patch to use a specific mod

since iam not able to write at general forum - because i dont own the game.
But the answer of this question is mandatory if i buy or not ^^

Is it possible to play only a specific patch (1.0.66477) so i can use a specific mod → better sp (im not interested to ever play online)

Mods aren’t officially supported, as far as I know. Actually, I don’t see that option yet.

Blizz doesn’t really care about the players anyway so idont need to have any official support.

Only need that specific game version.
Is it possible to downgrade from actual game version or something like in d2 days.

If you can buy an old copy of the game somewhere and patch it to the right version. Downgrading is your responsibility.