So for that specific prefix in filters;
I will just make chain = peer2-out , prefix= x.x.x.x/24, action = accept ?
And chain = peer1-out, prefix = x.x.x.x/24, action = discard ?
Essentially yes - but if i remember correctly if there's no rule to 'reject' your other prefixes then they will still be advertised - so if you ONLY want to do that /24 to peer2, then best bet will be to:
chain=peer2-out prefix=x.x.x.x/24 action=accept
chain=peer2-out prefix=0.0.0.0/0 action=discard
So this means that it will advertise /24 but then any other prefix you have active will get discarded for that peer.