Greenpassion, yeah, if they are healthy and growing good ,you can top them.
If not just bend them over 90degrees, and tie them down, and you will get way more colas, than topping, unless you top every branch.
Plus you don't even stress them much that way, that's how I do mine most of the time, this time, I ain't got much room, and I'm just trying these new seeds, for the first time.
Nebula has got great information about how to bend them over in her tutorials, really easy to do it that way, all your branches will grow straight up, it's easy to keep your canopy flat, so they all get equal amounts of light,.
Check that way out ole Bud. before you top them, plus you can still top them ,later if you want to.