Not sure what you mean by save?
You can already view the columns separately and they will be retained when you log out?
If it was account follows I'd suggest lists (https://fedi.tips/how-to-use-the-lists-feature-on-mastodon/) but that doesn't currently include hashtag follows.
Another approach might be to have totally separate accounts for different themes, that would give you completely different views of the Fediverse.