Split/rotted exterior timbers - What comes BEFORE the obvious

OK, dig out rot, apply wood hardener (good stuff, btw), spackle and paint. This I know.
But - the poor (decorative) 4x6’s (and the occasional 2x6) have been baking for close to 30 years - most are showing some splittting, a couple are beyound help.
Isn’t there something to “re-moisturize” the wood to keep it from splitting more?
My first thought was linseed oil - a quick review indicqates otherwise. Is there something to undo the lack of maintenance?

Is this treated wood?

1980’s tract house - (probably) dried doug fir (Home Depot et. al. weren’t yet spewing green lumber in all directions