Not quite sure of what you are trying to do. It looks like you are trying to change the logdir and thne you mention that the userexit will point to this directory.
First, if you are trying to change the log directory, then the manner in which you're doing it is correct. However, as instanceowner, can you touch a file in this directory? Go up a level from the current log directory and check it's permissions - does the new directory have the same set of permissions?
If you are trying to specify this path as the new archive log directory, then you do not need to specify newlogpath for that. The update to db2's db2uext2 should do that. However the permissions issue will need to be addressed.