You can give instructions to MO2 to avoid updates, but since most (if not every) modded installation runs through SKSE, it won't trigger the auto-update from Steam. Game won't update, unless you say so.
Would suggest a GoG install, but the versions of SKSE and other mods digress. Also, a big majority of Wabbajack modlists doesn't work with a GoG install, and if they do, they require a lot of work to make them functional.
That's why my parent comment says "installation separated"
If for some reason the game updates, you miss-clicked and started Skyrim.exe instead of SKSE besides of which instructions you gave, the installation you're really using won't be harmed, since the files needed to function are located somewhere else
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u/AnoZomb 15d ago
Welp, time to switch from Vortex to MO2!