You can do what you describe.
Here is an assembly of a Toggle clamp.
In the 'Assemblies' toolbar click on 'Wave Geometry Linker' this tool copies assembly parts into the work part.
When the dialogue opens select Type 'Body'
Select all parts of the assembly you want to copy to the work part and make sure you have 'Hide Original' checked.
You now have a copy of the parts in the work part.
Go to, File > Export > Part
Once the Export Part dialogue opens.
1. Specify the new part name
2. Select all the parts of the assembly you want to Export.
Check 'Remove Parameters'
Check 'Copy if Referenced'
You now have a single .prt file of your assembly, the parts in this file will not have any parameters and will not be associated with any other part.