I’ve heard people say that a tube with Slime sealant can’t be patched. However, I can assure you that I have patched them.
You may be asking yourself, why did I need to repair a self-repairing tube? In one case, I punctured the tube during installation. While Slime should seal punctures up to 1/8″ (3mm) the puncture was larger, so I had to patch it.
I found that the secret to patching a tube with Slime is to completely remove all residual sealant from the outside of the tube with soap and water before patching the it.