Editing imported object

Hi @Puresine Welcome to the Forum.

For anyone to properly advise please explain what you want to do achieve as the end result.

In this Thread the need was to alter 4 STL Mesh Seals and use the portions to create I Seal of the size needed:

https://discourse.shapr3d.com/t/subtract-from-mash/8827/17

Not being familiar with STL Files, unless someone else can help. this is the only way I know that they can be Edited is by Subtraction or Removal using a Closed Shape.
It seems highly unlikely that it can be disassembled.

From the ScreenShot the item seems to be a Trimmer Shield, if you have a Sketch of the Part it will be relatively easy to create a Body using S3D.

Happy S3Ding.