I am in the process of tearing down a Shimano Altus LT rear derailleur to clean and lube it (I know just soak it and clean it, but I enjoy breaking them down). I am stumped on how to relive the tension on the spring before I take it out. The stop for the cage is riveted into the body and can't be removed to release the tension. I guess I could just try to open the spring compartment but I don't think I would be able to reload the spring tension.
Has anyone ever broken down this derailleur? Any help is appreciated.

That particular one - no.
Have I taken apart derailers - yes.
Reassembly is a bit of a PITA.
Align the anchor point of the spring, twist, compress, lock down.
Contamination has to be real bad before it's worth it.

The contamination is bad but whether it's worth it is still to be decided. Thanks for your help. I may give it a try.