You will need to go through your solicitor for this in the first instance and ask them if it's possible or if they might go back to the insurer.
I will say if it's possible, it's the right call imo. Solicitors may often advise you to hold out for a few grand more as they'll also get a whole pile extra in fees if they win, but a few grand extra to you is really not usually worth the stress of two to it still stuck in your head when you want to move on.
With a lot of these kind of injuries, the awards are never really enough to compensate for the true human impact of them anyway, even in a best case scenario. So if it's an amount you can live with and covers your out-of-pocket expenses etc., from personal experience I'd always go with the easiest quickest solution because an extra five grand or so which may even be partly eaten up by extra legal costs that aren't covered by the respondent probably isn't worth it.