How can I remove unnecessary lines, surfaceses from one solid object group? Can I split a previously created group?
Hi- I’m not sure I understand, would be you be able to provide an example?
Or are these the same lines @Robert linked?
Hi,
you can create a new Shapes group. Tap on the “+” add a new group, and put the bodies you don’t need to that Group 
I am sorry it does not work 
Additionaly program in exporting files keep a lot unnessery junks… lines, shells… The ascii SAT format is more comfortable.
If you want those lines removed you can unite the different bodies (or is this one body?) with the the Union tool
This is one body.