What I then wonder is: if I do that, will those extra licenses remain when I re-add it to my mesh network? And then maybe 2 years later forced to unmesh it cause my RT2600AC died in one of my sites?Who's going to unmesh their MR2200ac and sign up for extra licences? On the chance that your current main router dies and takes your licences with it.
I told you M8, you have to think about UnifiI asked Synology about merging the free SSL-VPN client licence from my MR2200ac because it's a mesh access point controlled by my RT2600ac. The SSL-VPN, or any other service, is not running on mesh access points but it seems fair to let their free licences be temporarily assigned to the mesh controller's services.
I'm going to order a batch of licences to first see if I get serial numbers that I can save and assign to later devices. If that doesn't happen I'll then move my MR2200ac to access point mode and get licences. They are associated to devices via you account.