[franciscop]

Yes it is, IIRC I've given bounties to answers from long ago just to donate points to an answer that was really good. In fact it's in part exactly for this reason, since you can pick as one of the official reasons:

"Reward existing answer. One or more of the answers is exemplary and worthy of an additional bounty." - https://stackoverflow.blog/2011/09/23/bounty-reasons-and-pos...

[w-m]

Ok it's feasible, let me reword: it's awkward. You have to hunt for the "start a bounty" link in the question, not the answer, and then presumably still have the minimum bounty period of 24 hours, after which you have to come back to award it to the answer you wanted to reward?