Hi @Gertjan, thank you for answering. I´m not the only one, who is disappointed about openvpn makers suddenly treat their recent defaults as incompatible. As far as I know there is no easy (for people doing other stuff than openvpn too) documentation and/or recommendations for a soft transition.
I think the pfsense could be upgraded to 2.6.x easily, leaving the old vpn connections intact, but still using old standards. 2.7.x probably will not come up after upgrade if VPN connections were not altered before updating. But I don´t find any documentation, what to change to have a smooth transition from 2.6.x to 2.7.x.
"yust update to 2.7.2" is not a viable solution!
My hope was someone with knowledge about openvpn beyond using the wizards, could share some knowledge about paths for transition without interrupting vpn services for all who have to upgrade.