Hi @SamVanEenoo,
Actually I am talking about something completely different than what can be accomplished with the result tag…
I want to be able to copy details (input provided by the user) from one period to another.
Some other topic on this forum mentions how this works for the details on a account:
Every variable which has as name like: detail.custom.naam_variabele as a name will be copied from one period to another.
I was asking how this works for reconciliations, since they do not have a details drop.
In the meantime, I found out that it seems like the complete custom drop from the reconciliation is duplicated when copying the reconciliation details from one period to another, which is exactly how I hoped it would work 
My question can therefore be considered as resolved.