Octopus has a convenient feature to enable/disable things.
This makes sense when you don't want to get rid of something at the moment, but at the same time, you don't want it to be a part of your deployment pipeline.
For instance you can disable some legacy project (Settings-> Enabled-> No):
Or a deployment step:
Literally, any entity in Octopus could be enabled/disabled.
Don't forget to manage technical debt though. Don't leave a bunch of disabled things, they will pollute the environment. Ideally, get rid of them immediately. But if for some reason you need to disable them, schedule a technical debt user story or task to remove these guys later on.