Will it be possible to put DLC on pirates without losing save? (Fallout 4)

Yes

Already done.

Why not? What is hindering something?

sho means
there is no pirate right now, like pirates used to be, when they were with a translation from promt and a bunch of glitches
right now there are completely hacked, activated, translated and normally working repacks, with all dlts and patches
why put dlts on the old version if it's easier to download a new repack and install anew