Unfortunately it isn't possible to switch to super seeding without disconnecting everyone. After super seeding is turned on, Tixati has to send new "bitfield" message. According to Bittorrent protocol specification, this can be done only just after connecting a peer, before any other messages, so it has to disconnect them first.
Super seeding is meant for initial seeding a torrent, usually it's better not to super seed when a torrent is already distributed. Although super seeding in Tixati is well done, it can be slow for torrents with small piece size, especially if you have high upload bandwidth. With high upload you don't need this function anyway. Super seeding in Tixati depends on "have" messages from leeching peers, some clients don't send these messages to seeds in order to lower protocol overhead. Those programs most likely won't be able to download from a super seeding Tixati (qBittorrent for example).
The help page says:
Super Seeding
This setting is useful for initial seeding of a new swarm. This will force peers to download pieces in a well-distributed pattern, which reduces the amount of outgoing pieces that need to be sent before peers complete downloading and become additional seeds.
