run iptable changes without rebooting

I have a problem, I or we are running a script on a vps server and on this particular server netfilter-persistent is also installed. now if we run the script it doesnt work to use the ports, since the application that needs to ping it cant get access.

to be more clear, on the vps the netfilter is pre-installed so after we apply the new rules we also use:

iptables-save >/etc/iptables/rules.v4

ip6tables-save >/etc/iptables/rules.v6

but when the script is done it doesnt open the ports, but from understanding every change you make is instant? after we do a reboot it works but we would like to do it without having to reboot but untill now we didnt find the solution for it, we tried:

netfilter-persistent start, but its right after the saving of the rules, should netfilter-persistent start be working? or is there another command that restarts it without the need to reboot?

the reason we dont wanna reboot is that, well first let me tell you its to run nodes and some people run also other nodes so if we autoreboot it might or will stop peoples other nodes and we dont want that to happen.

but what basically is the problem is that we add firewall rules (ubuntu 16/18) and because of netfilter-persistent it doesnt work, only when we saved afterwards and rebooted.

I also have tried iptables-restore >/etc/iptables/rules.v4 but i have a feeling that is not the right command either

hope someone can give some inside)

thanks NooBie

edit: i see i made a mistake with the restore i see i used > but it should be <, so will test it now)