I can't give an answer, maybe you could endow a regular planet with a wormhole tag or sth, but it sounds like something that requires more enhanced modding, if it is even possible by non-devs. but I'd like to bring up something related ( ie I do some threadjacking)
is it possible to have dedicated star to star connections (again)? in some beta, there were phase lines even between stars, so you could not jump from any star to any other, but just to some specific ones. if that were possible, I'd like to play around a bit, such as to create a more freespace like gameplay (bc the wormhole option is a bit cumbersome and gets confusing due to the lack of lines). I mean, since it was there already, it might be possible to reactivate it without too much hassle.
bc for example I recently stared a game on vonruks labyrinth and it's really tough to play with suns and wormholes all over the place. taking the idea of just a handful of places in imminent danger (though more attackable through deep strikes and bypasses) that forms the core of phase lines to the interstellar level would be pretty neat for me. it's better with entrenchment, but you just cannot build sbs at every entrypoint, at least not moderately effective ones.