I don't know if this has been shared here before, but I am sharing it anyway. It appears to be old, but it is truly universal and decodes almost all files; certainly important dats.

 

Link: https://mega.nz/#!Wk0TSQyC!8PtJwpiumSF4BMfGTcJk1PeGXMl3CjxMGYuQx_mHjtg

no credits

The one from L2miko is fairly more uptated.

 

https://github.com/L2Miko/L2FileEdit

 

However, you will have some trouble opening some dats. I read in other post that you are fiddling around  with the 2.9 classic client, so a bunch of pretty important files wont open at all.

 

You will need this. It need some fixes related to file structure, but is the best that you can get for now (for free)

 

https://mega.nz/#!u05DTY6a!eUKIUIeMfiH37ZCWRvCS4Ktx0fn75LzIKA_N5B9h4Hs

I will add it to my collection. Thank you.