Custom activities can be used to record external asset lifecycle events. Activity IDs 1000 - 1099 have been reserved for user defined custom activities. Use RAMAsset.recordActivity(AssetActivity) to add a custom activity to an asset.
//Record a custom activity
CustomAssetActivity activity1 = new CustomAssetActivity();
activity1.setLabel("Activity Label");
activity1.setDescription("Activity Description");
activity1.setNumberData(1);
activity1.setTypeId(1010);
newAsset.recordActivity(activity1);
session.put(newAsset, new NullProgressMonitor());