Thanks for getting in touch! Unfortunately it’s not currently possible to make these selections for manual release creations sticky. Though it may be a great idea to suggest up on our UserVoice site! This is the main avenue we consult when considering future features/enhancements like this based on community support behind these ideas. https://octopusdeploy.uservoice.com/
Sorry it’s not better news for the time being. Don’t hesitate to reach out if you have any further questions going forward.