Confirmed on the latest dev build, the GUI system for editing trainers is un-optimized. Pressing OK does kick you out of the menu, meaning you have to navigate through all the screens again to get back to a specific place, instead of there just being a back and a save button.
Additionally, selecting some of the options in the menu such as "Custom Player Name" in the models section, will create a typing box that overlaps some of the other options.
I have sent this to internal so the devs can take a look and possibly come up with a more efficient and effective GUI. However, be aware, as there are more game breaking bugs in the beta, this will not be our #1 priority.
Thank you for your report!