It seems ship models from X3 Reunion computer game can be imported to 3D Studio Max, edited and saved in the default .3ds file format. Possibly also can be done using other 3D modeling software. Your best option is to consult some of the game moding forums and similar sites.
Convert X3 Reunion ship file to 3ds Max (3D Studio MAX) graphics.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert bod to 3ds on Windows
A widely-used 3D animation application from Autodesk
Convert from bod file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.