[Baldo_the_Don]

It's a bad idea to alter original game .pffs 'cause if you join any server, the alterations will be detected and you'll get kicked for sure, and possibly autobanned.

If you use a .pff tool, it's my preferred method to open the .pff, delete the file you mean to replace, close the .pff tool, reopen the .pff tool, reopen the .pff, then add the new file.

You don't need to reencrypt the new items.def. Well, not for DBHDTS 1.5.0.5, at least.

And for testing, you don't have to pack it into the .pff, just drop the items.def into the game folder and make sure you start the game with the /d tag. And always run any .exe for this game (the game, the installers, the updates, the mod installers, the pack.exe) as administrator. Executables without admin rights will have altered files (edited maps, mods, the dfv.cfg, the dfvplr.sav) shunted to a folder in the C:>Users>YOURNAME>AppData>Local>VirtualStore directory, and the game cannot access those files in that folder.

Reiterating the warning: Do not join multiplayer games with altered files in your game. Hosting a LAN serve and play is perfectly safe. I cannot confirm that hosting an online serve and play is safe, though.