Cheat Engine Method:
Depends on which boss. If its Oread then run CE open Dekaron.exe and search for this text:
Monster\oread\oread_ and replace all hits with this one donster\oread\oread_
You can do the same for Yoshima too:
Search: Monster\Yoshima_Diamechy\Yoshima_Diamechy_ and replace all with donster\Yoshima_Diamechy\Yoshima_Diamechy_
This will not work with Laiden Boss cause their spawn have the same animation but will work with any bosses or mobs.
CSV File Method:
Go to share\action\monster and search for oread csv files(must be 2 of them). After you found them open them and replace all lines that contains Monster\oread\oread_ with donster\oread\oread_.
You can do the same with Yoshima, Laiden etc
Enjoy.