You want to manipulate the target value when performing directory synchronisation and modifying attributes.

Directory synchronisation in PowerSyncPro focusses on using source attribute values to determine what the target value should be. 

The resultant target value for an attribute can be calculated from the result of a complex expression or simple expression, or you can do a direct copy in the mapping on the sync profile, any existing target value cannot be manipulated (using methods/functions) within the code of the expression you have created. So you would not be able to use targetValue.split, or targetValue.replace for example. 

You can reference targetValue without any other code, logic or functions. 

targetValue

But you are not able to perform any of the following

targetValue.<function>
targetValue.Split
targetValue.Replace
"HR " + targetValue

You can use code and methods/functions on source attributes or sourceValue to determine what we write to the target attribute, for example you can perform these 

sourceValue.Split('@')[0] + "@mydomain.com"
sourceValue.Replace(".","") 
userPrincipalName.Split('@')[0] + "@mydomain.com"

As an example, If you want to use the targetValue if the source attribute Value is empty or is null you might use this complex expression.