What makes you think you don't have the room for them? Descriptions indicating they grow much larger?

Sorry I should have explained. It’s getting too large for my small garden

You have other, already much bigger plants visible around it. And have you read how big non-dwarf cultivars of New Zealand flax get? So I continue to wonder why the particular focus on 'Little John'? All the more so because there is still plenty of unfilled bed space visible around it. Making that part of the bed look new and undeveloped rather than overgrown.

As far as details of pruning bottlebrushes go try searching the web for "pruning callistemon".

It sounds like your suggestion is to act like Elsa and “Let it Go” 😆.

I've never seen a C. "Little John" much larger than yours is now. They are a genuinely dwarf form. Pruning is generally at the soft tips, which encourages neater shaping and bushier growth and thus more flowers, but don't cut into the woody branches (unless you remove the entire branch back to the trunk).

And as with all Callistemons, prune off the spent flowers ever year.

Has it grown a lot since this photograph was taken?f The size looks fine and I can see a lot of open soil around it.

Yes, it can be pruned. I read that Bottlebrush blooms on new wood so you can prune it any time although I don't usually do anything drastic in hot weather.

It looks nice now so I would urge you to make other changes instead.

Actually I have several of these. I’ll post another one planted next to a dwarf olive that I also like to keep small. I’ve been pruning the soft tips and removing the new upward growth with success. But I can see that my strategy won’t last forever unless I eventually cut it back more severely. I won’t cut anything now in this horrible heat but doing research for the fall or early spring.