Hi Trebby I don't think mini tweaker will work on SH5 files. Among the "old" editors, S3d definitely opens them, but it can't handle some controllers which have changed format since SHIV. It can be used for tweaking the CollisionableObject controller though, which is where each unit's CrashDepth is set.
Should you want to used Goblin Editor instead, you should:
A couple of additional remarks:
Besides the CrashDepth setting in zon files, there is also a similar line in submarine's cfg file. Dunno which one of the two is applied (maybe the two are combined together);
IIRC, there seem to be a consistent discrepancy between the crash depth set in zon/cfg file and actual crash depth measured in game.