Is it possible to insert a condition like "= Today ()" into a row of a decision table?
There is no possibility to use such a condition in a decision table. To archive this goal you have to use literal expressions instead of decision tables:
Choose the element "Input data", name it somehow (e.g. "Enter Date") and set its attribute "Value Domain" to "Date"
Link it with the first decision (name it e.g. "Date Difference"), where you use the following expression: DayDiff(Today(), 'Enter Date')
Link the first decision with a second one where you can use the output of "Date Difference" for obtaining an output. If the "Date Difference" equals 0, then you are sure that the input date from "Enter Date" is today.