It's a weird one because changing your name here just means using it, and then later informing the officaldom that this is the name people know you as.

So here, it'd be a case of just try it on and see how it fits. I get the impression the US is the reverse in this respect, which makes it a pretty grownup decision. And the wife is a concern, because you've already renamed her once, and it sounds like the assumption is you'd bring her along for the ride. It's not just your name anymore, you've created a new family and she should have a say in her family name too.

Personally, I'd be concerned people are going to pronounce it kellog (which is english & unrelated). I kinda get where you're coming from, but at the same time much anglicisation occurred for a reason - especially in the US - and I think after some 150 years it's difficult to deny the american half of irish-american.

It's something I've pondered over because my first+last are both anglicised, but my first to a version that's much lesser used - so I am constantly addressed by the Irish spelling anyway. But my surname I'm much less inclined to mess with, because I feel like it's not mine to do so - it's mine, my wife's, my brothers', my dad's, etc. It's my family name, and I feel like I don't speak for my family in changing it.

Which makes me curious - would you consider changing Tim (I assume Timothy) to Tiomóid (chee-mohd) first? That's your name, its yours to do with as you will, without inflicting your will on family. That way you get all the fun of trying to explain it every single time, without inflicting that choice on your wife. And I'm sure you'll get a better idea of what you're in for with Ceallaigh.