It's not perfect, but hopefully someone will find this as useful as I have at times. If you've ever written something in 4/4 with a lot of triplets, only to realize that maybe it would've made sense to do it in 12/8 to begin with, you probably sigh and submit to the fact that you're going to have to spend time translating from one to the other, measure by measure. [insert infomercial music] Well, not any more!

There's a plugin in Sibelius called Convert Simple Time to Compound Time that can be found at Plugins > Notes and Rests. Basically, you just run this on whatever phrase of music you're wanting to converted, click Ok, Yes, then Ok, then you're good to go... as far as notes that are triplets go. All triplets will be converted, but it does have a few caveats.

You lose all lines and text (i.e. dynamics, lyrics, hairpins, etc.) Triplets are the only rhythms that get translated seamlessly. 4 16ths will be converted to 8th 8th 16th 16th, and other tuplets will either be deleted entirely or translated weirdly.

Like I said, it's not perfect, but if you really want to switch from a binary time signature to triple, this will at least save you some time.