wandering_vargr
It seems right now, that for the yellow(legendary) rewards, once me have them. We can still roll them on the draw pulls. It seems currently in the CBT at least we don't get anything back for this, it is just a purely wasted pull. It would be worth looking into some kind of exchange for when this occurs, if you do not intend to just remove them entirely from the list once obtained.
I would suggest that rerolling something you already have rewards a unique currency that can be built up to be used on more pulls or other unique items, like how genshin impact does it, or perhaps even have rerolls of items you already have count as a +2 to your 50/50 instead of just +1 like every other roll. Anything would be fine really, so long as we get something, though I wouldn't really recommend having it just give us the bare basic currency unless you intend for that currency to be able to buy more pulls to.
visual saddleBOT
drifting sleet