Well, you can prune it - I used to when I had one. It did get rather large, though!

the short answer is yes.
they are slow growing but keep on growing. at our local HPS we had a talk about 'dwarf' plants and the speaker showed a slide of conifers sold as 'dwarf' recently planted and then the same plants that were planted in 1902 50ft and taller. he was emphatic dwarf ie read slow growing but expect 3ft in 10-15 yrs.

I used to prune ours before we gave up and removed completely. Wear something with long sleeves and gloves and prune from underneath so it isn't visible. 10 years is about when they really start getting to big for their boots!

Great for Japanese Topiary if they have not
been touch before !

Topiary with a prostrate juniper?

yes ! and they look great !
Maybe more as bonsaii type if you prefer .

Hummm well not in my garden! When we finally removed the brute it was a good two metres in diameter and no higher than 50 centimetres!

My prostrate juniper gets a regular reduction to keep the size in check. As MG says, prune it from underneath to keep it looking natural. I don't want to remove mine as there is a borderline hardy tropaeolum polyphyllum planted under it - the juniper gives the tubers protection, and provide the perfect platform for the tropaeolum to ramble over