can you replace a 10 spd freehub body with an 11 speed freehub body to change your wheelset to an 11 speed ( from 10spd) without having to buy new wheels?

road?
what hubs?
maybe?

Yes but it all depends on which make and model of hub. Hope Pro 2 Evo is very simple for example, you need: XD driver

XD is only for SRAM 11sp, Shimano 11sp works on standard.

OP you need to be more specific. As you can see there are several correct answers dependant on your current spec.

With the likes of hope, maybe, with shimano i guess not.
I looked into this for my road wheels with hope hubs and it was possible for ome and not for others. It was something to do with the hub widths and the new freehub width.

Hope have published a list somewhere on their site. I don’t think others will be as helpful.

this is for a shimano dura ace c50 tub road wheel

this is for a shimano dura ace c50 tub road wheel

No, you can’t.