Sure it's possible. Once an object is added as a spaceship, it can be placed and moved manually with an in-game editor, or it can be fixed in a position on a catalog planet. The second part involves some scripting, but there are examples in the workshop showing how it can be done, or even in default game as it's used with LEMs on the Moon. You can see how it's done by looking at the scripts used with such objects.
There are some discussions related to this in the official DIscord server.
as for how to import a spaceship, or other objects, from 3d shapes in .OBJ format, it's mentioned in the manual https://spaceengine.org/manual/making-addons/creating-a-ship/
and in this guide: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1872025911