By definition a ringworld/sphereworld has a STAR at the center. This is what anchors it and gives it stability. Moving such a structure would require a coordinated move of BOTH the star in the center and the structure orbiting that star. Not simple, and obviously would require more than an "engine" facility on the orbiting structure. Given that the very existence of a ringworld or sphereworld is a science fiction concept requiring science we have not yet imagined, I guess we can't rule out the ability to move one to a race with the ability to build one...
But I think as a practial matter of game play it would be wise to NOT allow these to move with an engine facility. A huge planet packed with WPs would be the ultimate seige weapon for attacking a ringworld or sphereworld, though.