You can reset the volsize property of the dump device after a system is installed. For example:
# zfs set volsize=2G rpool/dump
# zfs get volsize rpool/dump
NAME PROPERTY VALUE SOURCE
rpool/dump volsize 2G -
If the current swap area is not in use, you can resize the size of the current swap volume, but you must reboot the system to see the increased swap space size.
# zfs get volsize rpool/swap
NAME PROPERTY VALUE SOURCE
rpool/swap volsize 4G local
# zfs set volsize=8g rpool/swap
# zfs get volsize rpool/swap
NAME PROPERTY VALUE SOURCE
rpool/swap volsize 8G local