WinSCP does not support automatic changing of owner of uploaded files.
For now, i use have setup a workaround. I use inotify to monitor the directory for changes and set the owner and group i want for changed files. Maybe there is another way, but for now it seems to do what i want.
I want to use a script to continuously update one of my directory's with a remote directory. However, at the remote directory user and group of the uploaded files must be different as the login user. For example, i login with username 'testuser1' via publickey. Now all my uploaded files are uploaded and owned by 'testuser1'. But they should have username 'usertest2'.