R.M. Meluch's Merrimack books
I found it in Powells, and I want to thank everyone who recommended these as they are precisely to my taste.
I have now read the first two only. There isn't a copy of the third one in Montreal, the fourth one is waiting on the shelf because I'm hoping there will be a copy of Sagittarius Command in Bakka next week -- and if not I'm going to give in and buy it online. I love them. They are awesome with extra awesome sauce. They are just exactly what I like even when it's trashy -- marines in spaaaaace, plus they are doing this amazing thing.
There's also Romans in space, which Meluch achieves by the astonishing method of having had the Roman Empire go underground in a conspiracy from the fall of Constantinople until there was a suitable planet, and then bang, off we all go to restart Rome. It's why we did Classics degrees, you know. It's ridiculous and over the top and totally cool. It's both awful and awesome at the same time. (And the only reason I can't believe this conspiracy is real is because if it was real, I would totally be in it.)
There's a real problem talking about the books though, which is that the thing that's really so absolutely brilliant about them, the thing that lifts them out of the category of "Romans in spaaaace books" and makes me crack my face smiling is a horrific spoiler of the kind that really is so much better if you come across it without knowing it's going to happen.
Also, do not read these books out of order.
Eventually, when I have read all of them, I'll read them all again and do a proper grown up post about them on Tor.com. But meanwhile...
Please please don't read further than this unless you have read The Myriad and Wolf Space. It won't tell you anything really, but you will get so much more out of reading The Myriad if you don't know this, I couldn't have it on my conscience to spoil you for it.
And please do NOT spoil me for anything further on.
So, the button gets reset into the "rational universe" at the end of the first book, and what Meluch does with the repercussions of "none of that happened" between there and the end of Wolf Star is just brilliant. I was reading Wolf Star on the bus on Friday and I just kept being delighted with it, with the swords, with the squid, with the insects going crazy, with the unresolved (in this universe) sexual tension.
You could read Wolf Star as a standalone, and there it would be, a fun fast adventure with marines and Romans and aliens in space, and you wouldn't see anything about what's so delightful. It's invisible if you haven't read The Myriad, and yet it would stand alone just fine, plotwise. It would just be ordinary. That's so clever!
I can't think of anything else that does this, that uses universe changing or time travel in this way, to create echoes and shadows and play with what the reader knows vs what the characters know. Or rather, I can't think of anything else that does this and makes it work even a bit.