These optimizations are termed partial SPF optimizations. IS-IS can be configured to perform a full SPF calculation when any network (non-topology) change occurs so that IS-IS always runs full SPF for all such network changes.
Note
If you disable the partial SPF optimizations, IS-IS automatically disables the incremental SPF optimizations and always runs full SPF. However, the reverse is not true: disabling incremental SPF optimizations does not disable partial optimizations.