Given that Invoices and Bills are a logical mirror of one another, we can manually raise them and set them both up to be recurring. All good.
We can duplicate invoices, but would be good if we could duplicate a Bill too just to save time - especially when there’s a number of lines and it’s just a couple of numbers that might change from “the last time”.
Hiya DochertyPartnership! 
Warm welcome to the API forum!
Reading your wee message here, it looks like your ask is more for the general FreeAgent app rather than one for our API specifically. We’d usually want a feature request like that placed with our Support team.
No worries though! - For this time, I’ve logged this feature request on your behalf. 
I hope this helps! I’m here and happy to lend more of a hand, so if you have any extra questions or ideas, don’t be a stranger! 
Have a lovely day!
Fiona