I don't know exactly the multiplier change yet but here are the main changes:
Annihilator could no longer be used with enchant burst stacking
Enchanted Grip no longer gives e burst buff
Enchant burst sword have reduced damage and is no longer unsheathe
Union Sword uses Atk+matk in its base damage calculation, it has reduced multiplier but overall higher damage.
Reunion sword have about 25% reduced damage, I suspect that the skill multiplier became 30 instead of it being formerly 40 mult. A single union- reunion sword have about 10% reduced damage compares to pre adjustments. But this is with full matk build. SRD build will suffer more.
Maximizing Matk is the way to go, even getting Prayer in a combo gives you an edge even if it only has 25sec duration. but as long as you can cycle it it's sustainable. Prayer with Magic device gives you 15% matk, about 600 matk with my stats
Using Union Sword without the reunion is a good option since it has better damage now. So instead of using up all the enchanted burst buff you can use only 30 sec timer each time you use Union.
Even Union without instant cast is a decent standalone damage skill, which means that even if you want to do union on staff md mage, you'd deal nice damage. You only nead decent motion speed. Staff md can use enchanted barriers to supplement motion speed whilst ohs md can use trigslash