Simple arithmetic on dates can be done with the date defined as xs:date and the increment as xs:duration
(see here) so adding 5 years to the current date is created in mapper as:
current-dateTime()+"P5Y"
[UPDATE ... while you can enter that ok into mapper, or assign a "P5Y" into a duration type variable, the result does not execute ... I get
current-date() + $dur)}": Error while executing an XPath expression: net.sf.saxon.trans.DynamicError: Unsuitable operands for arithmetic operation (xs:date, xdt:untypedAtomic)]