I get your point. Indeed at XY problem, given that there probably are better solutions for this
The goal here was to create a "mapper" from one data source (a data structure from another system) to another (a data structure that "fits" in my system). Something like this:

[% destination.header.address.surname         = source.orderData.custI
+nfo.surname %]
[% destination.header.timestamps.created     = methods.tounixtime(sour
+ce.orderData.orderDate) %]
[download]

This results in a hash structure that is converted to the format my system expects. I.e. So yes, I'm using Template Toolkit to manipulate/process data.

I would agree that TT isn't a good solution for this from a developers point of view. But the end result is _exactly_ what I'm looking for, a simple "configuration file" where the intended user (a system admin that sometimes dynamically needs to change/add fields) can do what he/she needs. If I could find a better solution for it, I would use it ;-)