We have options built into WF to automatically update project timelines each night.
It would be great to have a similar facility to update all calculated custom expressions or perhaps subsets thereof.
We use a number of calculated fields that compare the current date to task dates and baseline dates. We report on them and conditionally format based on values.
A possibility is to put the custom expressions in report columns. These always produce an updated result when the report is run. However you can't do condition formatting on an expression. Hence the need to put the expression on tasks, report on the field value and conditionally format based on the value.