Yes, I am using Trace.File with needed path. The question was about changing the default path, but it is not relevant anymore—tracing to a custom path is working as intended. Thank you for answering!
But it is still interesting about changing default path.
Also, maybe someone now commandline argument which tells Unreal to not start tracing automatically when starting Engine or Development Client? It is something like this -tracenoautostart, but unfortunately it is all I can remember. It exists; I know it because seen it.